She knew he was a little strange when she first met him. It made him, perhaps, more lovable. But who want to know until they daily shared a bathroom that every time he took a shower, he put a wash cloth over his face because he couldn't stand the beating water.

She, too, had her quirks, not revealed to him until they became roommates. When she ate meat and potatoes and peas, she ate one pea with every forkful of meat and refused to finish the meal if she ran out of peas. She stood by that rule.

They loved each other. But could that love last, when she was compulsively concerned about the germs on the back of her hand, and he couldn't go to sleep until he'd stashed his underwear under his pillow?

Suddenly, each was face-to-face with the private routines and unconscious games of another human being with rules for the way to eat, sleep, shave, put on clothes and count money. Rules for the proper way to squeeze the toothpaste, to roll the toilet paper.

Toothpaste and toilet paper, in fact, are the primary and secondary causes of broken marriages, according to quirk collector Judy Reiser. (Toilet's paper is first.)

"If she likes it going over the front of the roll and he likes it going over the back, of is she squeezes the tube from the middle and he squeezes from the bottom, those are grounds for divorce in my book. What do you think 'Irreconcilable Differences' means, anyway?"

Reiser, 31, a New York City art director, became interested in quirks when she was telling a friend about how she's always been concerned about germs on a coffee cup. So, on the premise that most people pick up the cup with their right hand, she always uses her left, thus avoiding, at least, the right-handers' germs.

Her friend responded with an equally ridiculous private rule.

Since then, Reiser has collected about 500 idiosyncracies from, among others, junior high school teachers, financial analysts, printers, receptionists, store owners. Her book, And I Thought I Was Crazy! (A Fireside Book by Simon and Schuster, 138 pages, $4.95), attempts to reassure quirk-crazy readers by reporting other people's small -- but real -- insanities.

There is the ad agency man, for example, who has to lace his shoes with equal tension: If one is tighter then the other he ties them again.

The 28-year-old saleswoman who can't stand to have anyone, even her husband, touch her pillow.

Reiser found that quirks cut across the boundaries of sex, income, race and marital status.

"Everybody has them, but most people don't realize it. They just never think about it."

Reiser got grown people with responsible jobs to think about it, and apparently with little embarrassment, to tell her about it: like the sound engineer, 33, who has a difficult time making love to a woman unless she's lying on his right side.

"I think people do these things so they can cope with life easier," says Reiser. "It puts one part of their life in order."

She hates, for one thing, to throw a piece of garbage into a clean wastebasket. "I was relieved to find that other people have the same quirks I do."

What you're doing in the privacy of your own home may, of course, be driving your mate up the wall.

Could you live with a man, for example, who, usually sleeps head-to-head with his wife, but during a full moon sleeps head-to-foot because he's afraid he'll wake up in the middle of the night and bite her neck?

"Quirk compatibility," says Reiser, "is essential among couples. The next time you're at a party, instead of asking, 'Are you a Leo,' find out whether he's a Folder or a Crumpler. It's a good way to avoid serious problems in a relationship."

(According to an airline ticket agent Reiser interviewed, there are three kinds of people in the world: Folders, Crumplers and Rollers.)

Serious problems also might be avoided by keeping your mate's strangest quirks secret. The only worse thing than having a truly strange quirk is having a mate who talks about it. When you're out to dinner with another couple and your mate begins, "Oh, that reminds me of the way my husband . . .", you know something "cute" you do is about to become a part of the evening's entertainment.

Bathroom quirks, claims Reiser, strike even the best of us. Some of your closest friends may refuse to use public facilities, others only when the faucet is turned on. Etiquette adviser Emily Post never told you, but Reiser does, that it is acceptable to be a Reader or a Non-Reader, a Single-Flusher or a double-Flusher.

"But under no circumstances is it acceptable to leave the toilet seat up in the middle of the night, or the shower on when the water is turned off."

There are people, says Reiser, standing alone in bathrooms everywhere trying to figure out how to deal with another's toothbrush.

"My friend dries his toothbrush every morning because he hates when the excess water dribbles off the brush and leaves a white film on the side of the toothbrush rack. He's meticulously clean. He recently got married and how he dries his wife's toothbrush, too, because she refuses to do it."

And "It's amazing what we take to bed with us," say Reiser. "Dozens of pillows -- three under your head, two over your head, one to hug, four to line up next to you. Stuffed animals and live animals."

Some other quirks, all from Reiser's book (as are the rest in this story):

"For five years, my bed was perpendicular to the wall. Now my apartment is being redone and the bed has been built into a platform and it is now parallel to the wall. I still sleep perpendicular to the wall across the short side of the bed. It creates too much confusion within my body to adjust to the new direction so I let my feet hang over." -- Partner in a commodity brokerage firm, male, 30.

"I bite off the ends of hot dogs and throw them out before I eat them. I just don't like the look of them. I do the same with pickles."

--

"Every time I cash my paycheck, I smell each bill before putting it in my wallet." -- Librarian, 23, male.

"I pick up the groceries in the supermarket in the order that they're written on my list. If the bread and the cereal are next to each other in the same aisle but not one after the other on my list, I will go past the cereal and come back for it later when I reach it on my list." -- Actress, 28.

There are the sock-sock-shoe-shoe people, as opposed to the sock-shoe-sock-shoe types; those compelled to count cracks in the sidewalk, and people who have to be the last to hang up on the telephone.

There are some quirks that you don't, of course, talk about.

About the most ingenious varieties, says Reiser, "People will either think you fondly because of them, or it will irk the hell out of them, and they won't want anything to do with you."

The best solution to food quirks, she says, is to associate with people who appreciate your strangeness, your "individual style . . . If you like to eat off of someone else's plate, find someone who enjoys eating off of yours."

To simulate on overall normalcy?

"Hang out with people who are quirkier than you."

With, for example, this 28-year-old photographer:

For all my life, at least from my earliest recollection, it's been physically impossible for me to fall asleep without my navel being covered. If it's summer and I'm naked, I still have to have a part of the sheet come across my navel or I can't sleep."