WITH THE COOL authority of a tailor draping a bolt of Harris tweed over a potential customer, Stan Cohen says, "{Flatulence} is very popular today." Of course, he doesn't use a euphemism to describe one of the more common sounds in practical jokedom.

To illustrate, Cohen blows up a whoopee cushion, lays it on the counter at Al's Magic and Fun Shop and depresses the bloated bladder with his palm. Blrraaaaaap! Yep, it's easy to see that a gas gag is an essential part of the well-dressed joker's wardrobe.

For the practical joker who doesn't have the time or inclination to drywall his boss's office shut or fill his brother-in-law's car with smoked baby clams, there are magic shop novelties, off-the-rack gags that for less than five bucks will shock, squirt, discolor or disgust just about any unsuspecting sucker.

There are squirting flowers, squirting calculators, squirting rings, shocking lighters, shocking books, shocking beer cans, gum that turns your tongue red, gum that turns your tongue blue, onion gum, garlic gum, red pepper gum, rubber vomit, rubber dog do.

"Rubber items are very big," Cohen says, again the haberdasher. "Snakes, spiders, rats . . . vermin of any type made in rubber."

Like a good tailor in search of just the right cloth, Cohen searches far and wide for his novelties. "Germany's famous for stink bombs. They like stinky stuff. The English are very big on {breaking wind}. They make a good stink perfume. A lot of the good gum comes from France."

His own favorite gag depends on the situation. For a while he was into Snap Snot, a stringy length of silicone that's inserted into the nostril and expelled in a mock sneeze. "The shocking beer can's probably my favorite right now. I like the dog do, too. I've probably pulled that one more than anything else."

Cohen does good gag business year round, with the expected upsurge around April Fools and Halloween, but the industry has changed in the 54 years since his grandfather founded the shop. "In the old days a lot of {the gags} involved pins . . . . You'd reach into a box and a lance would stick you."

He doesn't, when he says this, sound entirely disappointed that those days are over, but Cohen is quick to point out that the fear of litigation is driving some of the best practical jokers into retirement.

"A lot of practical jokes have gone off the market," he sighs. "In 10 years there might be not too many of them left because people have gotten so sue-crazy."

The real exploding cigars -- the kind packed with a charge and a spring that sprongs them into that classic peeled banana shape -- have been off the market for years. Sparkling matches are about as common as spats. Cigarette loads are going the way of cigarette smokers. You can still get German itching powder (Juckpulver) but the best itching powder -- Itchicoo, made in England from the ground tips of the nettle plant -- was so strong that it too is gone.

Still . . . "Roaches are always good. There's nothing more repulsive than a roach in your food."