Groucho Marx knew something about groups: "I would never want to belong to any club that would have someone like me for a member."

Groucho wouldn't have joined the Marx Brothers Study Unit. Nor would he have become a member of Pickle Packers International, the Andy Griffith Show Rerun Watchers Club, Procrastinators Club of America, the Visual Lunacy Society or the Dedicated Wooden Money Collectors.

Millions of others, however, have joined either these or one of the 18,942 other nonprofit groups in the Encyclopedia of Associations. From the American Astronomical Association to the Flat Earth Research Society, there's a club for all tastes.

The more eclectic the organization, the more likely it is to run on sheer willpower -- and become defunct with the speed of a post office box snapping shut. Here are nine groups that are still around: International Dull Folks, Unlimited

"I knew I had been searching for something all my life, and a couple of years ago, I found it," says J.D. Stewart.

That something was the philosophy of dullness, which Stewart embraced with an undullish fervor. He joined a now-defunct dull men's club in San Francisco and, when he saw they were only kidding, formed a splinter movement in his home town of Rochester, N.Y. -- a city, he says with a touch of pride, "that is the dull capital of the world. You don't boogie too much here."

The dullness practiced by International Dull Folks, Unlimited is related to life style, not mental ability.

"We don't follow trends, fads or foolish fashions. We just do our jobs faithfully and well. We like to smell the compost pile along the way, spend time with our families, play with the dog, and tune up the old Chevy," says the 51-year-old Stewart, a statistical analyst ("Statistics, along with accounting, is in a class by itself for dullness").

In his spare time Stewart sends out the Snooze News to the club's 700 members, maintains the IDFUN library (a Roget's Thesaurus and a dictionary), and follows an appropriate life style: dull meal, beans and franks; dull motto, "in vinum veritas" (loosely translated as "in generic beer is truth"); dull sport, bowling; dull evening, home movies and slide soire'es; dull symbol, the generic product code; dull rallying cry, "Enthusiasm wanes, but dullness is forever."

For more information: J.D. (Dull) Stewart, Chairman of the Bored, IDFUN, P.O. Box 23584, Rochester, N.Y. 14692. Couch Potatoes

"Excessive TV viewing is relaxing," says Robert Armstrong. "It's the indigenous American form of meditation."

The 35-year-old free-lance California cartoonist and illustrator watches 60 hours a week, give or take a few sitcoms, on his 10 TVs: "Five in the front viewing module; two in the kitchen; one in the bathroom, of course; one in the bedroom; and one in the garage."

It all started back in '51, when Armstrong's parents bought their first set. "I watched as much TV as I possibly could, and eventually realized it was probably the best way I could spend my time," he says.

In the mid-'60s, Armstrong discovered that several friends shared his viewing enthusiasm for "Lost in Space." They formed the Couch Potatoes (the tuber, after all, has quite a few eyes), an informal group that went public in 1976 and now claims 5,000 members.

"People try and talk me out of watching, but they've never offered any good alternatives," Armstrong says. Besides, "it's good ecologically to watch as much TV as possible. You're not driving around polluting the air, and it provides more parking spaces downtown for the jerks that are."

The Couch Potatoes publish an irregular newsletter, Tuber's Voice. In a recent issue: "Lawrence Welk: The White Man's Soul Train?," a listing of ideal TV shows ("The Dark Side of Mr. Rogers," "Return to Long Island," "That's Inedible!" and "Das Love Boot"), and recipes from Chef Aldo, the Station Break Gourmet.

Most of Aldo's snacks are designed to be made in under three minutes in a couch-side toaster oven. Like the coffee crystal sandwich: Take a slice of white bread, spread with margarine, sprinkle with freeze-dried coffee crystals and pop in toaster. If desired, top with sugar and Cremora. "Perfect," Armstrong says, "for late-night B movies."

Another newsletter feature: Dr. Davenport H. Spudd's advice column -- when is it okay to talk or change the channel, is it necessary to wash a TV dinner tray before using it as a UHF antenna. And there's "Big Brother Is Watching With You," a feature for Tater Tots.

How can Armstrong afford to watch so much TV? "I lead a very spartan existence." Money is spent only on essentials: electric bill, TV Guide subscription, snacks.

"I'm a televisionary," he says. "When you watch so much, it all becomes good." The slogan of the Couch Potatoes: "There's no such thing as a bad TV show."

Couch Potatoes, P.O. Box 249, Dixon, Calif. 95620. Send a stamped, self-addressed envelope. International Porlock Society

Coleridge, interrupted during the composition of "Kubla Khan" by a person from the nearby English town of Porlock, later couldn't remember what he had been intending to write.

That anonymous Porlockian who unwittingly caused the poet to falter has now acquired his own following. But these days, when the International Porlock Society interrupts someone, it's intentional.

"We call attention to the fact that everything published isn't necessarily worth publishing," says Russell Meyer, an associate professor of English at the University of Missouri and the society's secretary. "Even people you like can go on at too much length."

Most of the society's interrupting goes on at scholarly conferences, especially its own annual meeting. "We have two techniques: the chair shuffle and the prolonged cough," says Meyer, 44. The second is especially effective, he reports: when 30 or 40 people are coughing, the speaker usually takes the hint.

The society's journal, Cogito Interruptus, is impossibly erudite for anyone unfamiliar with the 16th-century English poet Edmund Spenser, whose interrupted works are taught by most of the Porlocks. Owing to interruptions, the '78 issue came out in '81; the '79 issue is promised for sometime this year.

Until then, Meyer has other projects. "I chair the imperfect subjunctive section," he says. "We interrupt works that are already finished."

Porlock Society, c/o Russell Meyer, Dept. of English, University of Missouri, Columbia, Mo. 65211. The Unicorn, Ltd. Conglomerate

An old joke says northern Michigan has nine months of snow and three months of poor sledding, a condition that might help explain the proliferation of organizations at Lake Superior State College in Sault Ste. Marie.

The umbrella conglomerate for the 20 groups and related annual events is the Unicorn Hunters, dedicated to the proposition that every man has a unicorn he is predestined to hunt.

The Hunters draw three types of people, says W.T. Rabe, the school's public relations director. ''There are people who thint it's funny to hunt for something that doesn't exist; there are those who collect unicorn artifacts; and there's the philosophical side -- the quest is part of man seeking the meaning of life, getting your head together.''

Rabe, 63, is ''the archivist -- I keep track of what's going on.'' Among other activities, the Hunters burn a snowman at the end of winter, celebrate Lizzie Borden liberation day and write-a-love-poem fortnight, and participate in the following associations:

* Punsters Unlimited. Assigns serial numbers to submitted puns. Cited as exemplars: 'Though he's not very humble, there's no police like Holmes'' and, in a remark attributed to Nero, ''Though it's beginning to crumble, there's no blaze like Rome.''

* Passenger Pigeon Bird Watch/Count. Purpose: ''to verify that the passenger pigeon, which numbered in the millions, may be extinct, as believed.''

* International Open Stone-Skipping Tournament, sponsored by the Stone-Skipping and Gerplunking Club. The tournament is on Mackinac Island, Mich., on July 4. Current record: 24 skips. Winner gets a 75-pound rock with his name on it.

W.T. Rabe, Lake Superior State College, Sault Ste. Marie, Mich. 49783. Fifty cents hould be sent per organization to help cover mailing costs. Diastematic Club of America

''No one should be ashamed of a space between his two front teeth,'' says Dale Hempel. ''What God has given no orthodontist should take away.''

Hempel, school superintendent in Moses Lake, Wash., says the 3-year-old Diastematic Club ''started out as a joke, but some of the letters we get back are rather tear-jerking -- people saying they have been ashamed all their lives of their gap.''

The requirement for joining the 350-member club is at least 2 millimeters of space between your two front teeth -- the size of a round toothpick. In addition, you must never hide your gap, never wear braces, promise never to completely clear the kernels from an ear of corn and must enter all spitting contests, liquid and seed.

''We're a vansihing breed,'' says the 50-year-old Hempel, who is planning a Diastematic get-together at Union Gap, Wash. ''Soon because of orthodontic improvements, not many people will have gaps.''

In the meantime, he says, ''I can get a mouthful of water 8 feet.''

Diastematic Club of America, P.O. Box 1075, Moses Lake, Wash. 98837. Absent-Minded Club

Several years ago, Bob Gwynn says, "I was taking my wife out to a club, and John DeLorean was there, and I couldn't remember his name. I said, 'Honey, you know who this is,' and she said, 'I don't know who it is.' . . . I made a fool of myself."

It's a familiar scene: Someone comes up to you, greets you and acts like an old friend. Why can't you remember his name?

"I always wondered why people didn't start an organization for those who, like myself, have a lapse of memory," says Gwynn, a clothing store owner. "If there was a club, people would forgive you for forgetting their name."

Gywnn, fool no more, formed the Absent-Minded Club in 1982. Membership is $15, half of which goes to the Michigan Humane Society ("It's a good cause, and I like animals," says Gwynn). Members receive a forgetter's lament and a little pin of Rodin's Thinker -- the key to the whole operation.

"Instead of standing around like an idiot when you've forgotten someone's name," says Gwynn, 56, "you show your pin, stick out your hand and say, 'Hello, colleague.' He should immediately forgive you and tell you his name."

Bob Gwynn, Absent-Minded Club, 112 S. Woodward Ave., Birmingham, Mich. 48011. Burlington Liar's Club

"I honed my hunting knife to such an edge that when I removed it from its scabbard, the shadow of the blade lopped off two kitchen table legs and a ceiling fan blade before I could reach the light switch."

So claims George Covington of Clinton, La., and his story was good enough for the Burlington Liar's Club to name him last year's World Champion Liar.

The Liar's Club stretches back to 1929. Disbanded in 1980, it was reorganized in 1981 to "keep the practice of telling whoppers going," says club vice president Donald Reed.

In 1984, they had 300 entries, from which Covington was selected the winner on New Year's Eve. "We look for originality, a good laugh, and personally, I like them short," says Reed, 67. Politicians are barred from competition -- "This club is only for amateurs."

But that doesn't mean politicians can't be the target. As the 1979 winner has it: "It was so cold in Missouri last winter that I saw a politician standing on a street corner with his hands in his own pockets."

The first champion liar, incidentally, was a Burlington police chief. Asked to compete, he replied: "Me? Why, I never told a lie in my life." He was unanimously selected.

To join, send $1 and a lie to Donald Reed, 149 N. Oakland Ave., Burlington, Wis. 53105. Jim Smith Society

"I never met a Jim Smith I didn't like," says James H. Smith Jr.

He's met more than his share, too: 250, at last count. But there was a time when he was bothered by the name.

"I used to be a police reporter. In the slow times, when we sat around chewing the fat, I got ribbed -- 'Are you sure that's your right name?' This went on for years, until I thought it might be nice to have a card to pull out, and say I was a solid gold Jim Smith."

In 1969, he formed the Jim Smith Society. Now there are 1,263 members, including seven females (variously named Jamie, Jimmie and Jimanne). "We're a fun-loving group," says Smith, 64. Now retired, he's working on a book, Jim Smith: Greatest of the Common Names.

Get-togethers can be confusing. "If someone called out 'Jim,' 60 or 70 heads would turn simultaneously," says Smith. "So we call each other by our home towns -- Dayton, Dearborn, Oil City, Danville." One advantage to the society: "When we play ball, we don't need a scorecard."

Jim Smith Society, 2016 Milltown Rd., Camp Hill, Pa. 17011. Irwin Allen Fan Club

For David Krinsky, the golden age of television was between the ages of 5 and 10, when he watched "Lost in Space," "Time Tunnel," "Voyage to the Botton of the Sea" and "Land of the Giants."

It's no accident that all four shows were the creation of Irwin Allen. Claims Krinsky: "Allen had a certain feel for fantasy and science fiction that, for sheer innocence, no one else could capture. He didn't produce them as if the viewer was a 12-year-old, even if the viewers were 12-year-olds."

So great was Krinsky's esteem for Allen's work that in 1973 -- when he was 12 years old -- he cofounded the Irwin Allen Fan Club, which now has 450 members. The club issues a quarterly fanzine that profiles the shows and their stars and presents new fiction based on the series.

The important thing about all four shows is their quality of "humanistic science fiction on a simple, innocent level. They are as important an artistic statement as Kubrick's '2001,' " he says.

Take the character of "Dr. Smith" on "Lost in Space." As played by Jonathan Harris, Krinsky points out, "Smith is an antihero, the only scared, cowardly, greedy person who was made a star of a TV series that children loved."

Krinsky, despite his relative youth, has done some TV watching in his time. With club codirector Joel Eisner he wrote Television Comedy Series, a 900-page compilation that details every episode of every syndicated television comedy series from 1949 to 1980. "But I'm not a TV addict," he says. "I don't spend all my time watching."

And what does Allen think of all this adulation?

"Irwin," says Krinsky carefully, "wants as little to do with us as possible."

Irwin Allen Fan Club, c/o Joel Eisner, 2111 E. 65th St., Brooklyn, N.Y. 11234.