There's something about 40th birthdays that sets them apart from the others. Sure, people make a fuss over 30, 50 and other milestone birthdays. But at 40, gallows humor sets in. We celebrate still being alive. It's a time to reflect on past deeds, on deeds never done, on deeds we're gonna do if it kills us. It breeds a daring, a craziness, a willingness to take chances with other people's self-esteem.

What other birthday brings out the creative genius in guests as well as party givers? Guests come dressed in mourning, they create poems, compose songs. They pay for weird personages to descend on the guest of honor to embarrass the daylights out of him or her.

Teetering there at the midpoint of life, we need an extra something for the next 40 years. Some primitive instinct must lead us to create this rite of passage, to administer this balm. Beyond the mandatory laxatives, Geritol, liniment, and denture cream, here are some suggestions to join in the 40s fun:

Surprise parties. If you really want them to be surprised, consider throwing the party long before or after the birth date. (Forty-year-olds are very suspicious.) If afterward, you'll need some other bona fide birthday celebration to throw them off the scent.

For my husband, the kids and I concocted a little treasure hunt. He found black balloons and a note in his car after work sending him on an odyssey to an old teen-age haunt for hors d'oeuvres (greasy onion rings), to a hot tub (champagne, The Ruba'iya't, and swimming trunks waited) for a meditative soak, to a hilltop cemetery to confront his mortality and read his future as we'd predicted it in fortune cookies, and then home to his own personal treasure -- us! I was sure after that elaborate red herring he'd never expect a surprise party, but he was still suspicious.

(A note of caution. If your victim has just undergone a trauma, even if it is resolved, even if you already invited 100 people before it started, be cautious about imposing upon an emotionally drained person. They may find it frivolous and be unable to muster a celebratory spirit. Better to send 100 postponements.)

Let's hear it for quiet romantic surprises, too. One woman spirited away her husband in the car and announced they were going on a trip. All the way there, he enjoyed trying to guess their destination. How about a glider ride or a visit to your old parking spot?

You can hire a surprise. Strippers are popular, observes Jonathan Eastman of Celebrations in Kensington, but for 40th birthdays, they want more than just regular strippers. Hire a gorilla or a "Tootsie" type act. The loonier the better.

Before sending a "bodygram," however, ask for a demonstration. A belly dancer might be a hit with your friend, the minister, at a small party of close friends. In front of the whole congregation, it's another story. You want to create moments they want to remember, not ones they can't forget.

Period parties. One hostess had a sock hop in a high-school cafeteria, where the guests all wore '50s outfits and the centerpieces were old car parts. Or let your friends dig out their beads and bell-bottoms and recreate a psychedelic scene.

A 40th party can be planned around just about any activity, like a car rally, with the clues all about the birthday person, a scavenger hunt for items from the celebrant's past, tubing, a picnic or, around here, a crab feast.

Thanks to modern technology you can blow up baby pictures to poster size and hang them from the ceiling all over the room. At one party, the 40-year-old faced a sea of guests all wearing T-shirts with his computer-reproduced "photograph."

Stage a "This Is Your Life" production using real surprise celebrities from the person's life, or dress up and pretend to be old lady Grimbat who sent her home from school because her skirt was too short.

With video camera or slide projector you literally can look down memory lane. Film footage or still photos can be transferred to videotape. It's moving to see a life progress before you in a matter of minutes.

Ask guests to bring something meaningful to put into a scrapbook, to write in a memory book, to make a prediction for his future.

Once you open the door to guests' spontaneity, step back and be ready to go with the flow. Your guests' creative enthusiasm and expressions of esteem, serious or insulting, will be treasured memories.

It's all in the name of "I care about you. For the first 40 years, you did good. Here's to 40 more." Like the woman that came home to see a giant banner over her house saying: "For a good time call Susan, phone number ... "

Ellen Nibali, a Columbia free-lance writer, is looking forward to her 40th birthday.