You know those silly social taboos against suffocating your mother or having sex with your brother's girlfriend or exposing yourself to your grown children? Fugeddaboutem! Feel free to express yourself: Smother! Copulate! And let's see what you got under the nightie! Live, in other words, as the low-rent Feinsteins do in "Lenny & Lou," Ian Cohen's smutty-funny cesspool of unbridled outer-borough neurosis.

This Woolly Mammoth production, a world premiere directed with a fastballer's dexterity by Tom Prewitt, is comedy gone mental, the sort that asks the crucial question, What if the Oedipal and assorted other complexes and anxieties of a repressed Jewish family from Sheepshead Bay could be unleashed as if they were the contents of Pandora's Box?

In such a play, no stunt is too shocking, and "Lenny & Lou," with its potty mouth and steady stream of uninhibited displays, positively pleads for the title of Dirtiest Show in Town. It's not pornographic exactly, though one scene of acrobatic rutting is so well choreographed it would make a decent novelty act in an X-rated Cirque du Soleil. No, "Lenny & Lou" is merely reveling in a vision of family life in which the id has been liberated, like a big, slobbery golden retriever romping in the backyard.

Vulgar is the word, and sometimes Cohen points the shenanigans in the direction of the baldly sophomoric. He's too much the gross-out king testing the limits, for instance, when he has Lenny (Howard Shalwitz) tell us of his brother Lou's (Michael Russotto) childhood preoccupation with the flotsam in his nose. Nevertheless, Cohen is a swell composer of comic crises -- at times "Lenny & Lou" borrows imaginatively from the conventions of farce -- and the risible lines he gives these actors crackle with a buoyant authenticity. The play practically defines guilty pleasure.

Cohen's dialogue is spoken with an antic zest by Prewitt's cast, which -- with one surprising exception -- is smashingly up to the assignment. Shalwitz, especially, is spectacular. Playing a sleazy, schnooky bank employee who imagines himself an undiscovered rock legend, Shalwitz is so in his element in Lenny's oily skin that you can positively smell the performance. The hollow-eyed gaze, the praying-mantis posture, the greasy hair, the black polish on the bitten-down nails (nice touch) imbue him with the look of one of those dazed deadheads you see lingering outside a 7-Eleven at odd hours, inhaling a can of beer.

Russotto's Lou is a sweet, whiny loser, such a schlep he makes Lenny seem a veritable Jude Law, and Jennifer Mendenhall (what type can't this actress play?) brings the necessary from-the-old-neighborhood hard shell to Lenny's Italian American wife, Julie. Erika Rose contributes a fresh and feisty performance as a West Indian cleaning woman with a firm moral grasp of the universe. Only the usually sure-footed Nancy Robinette is wobbly here, playing a senile Jewish shrew from deepest Brooklyn, a part that is beyond the scope of her natural gifts.

"Lenny & Lou" offers a seriously twisted account of a patented family dynamic, the rivalry between a pair of brothers for a mother's love. In this case, the mother, Fran, played by Robinette, is an absolute witch, her dementia exacerbating her worst instincts. She has strung her grown-up sons along on a river of guilt and uncomfortably unresolved sexual feelings -- the Freudian element is unmistakable in her demand that they bring bananas, purportedly to help her digestion, when they visit her -- and now that she is less able to discern fantasy from reality, her impulses have become more graphic and cruel.

What sets the dizzy plot of "Lenny & Lou" in motion is a violent, cathartic act by Lou that, in a sense, consummates his love-hate relationship with his mother, who has always favored the older son, Lenny. The play drops more than subtle hints of a confused and bizarre attachment between Fran and Lenny; Lenny is both a sex addict -- which seems to suit Mendenhall's randy Julie just fine -- and a mama's boy who evinces a strange affection for his mother's clothing.

Robinette is the least convincing player in this frantic comedy because, despite her best efforts, her energy is all positive. (She's also at least 20 years too young for the role.) She can't help it; her dithering stage persona is essentially lovable, and Fran has to be an unmitigated downer, a destructive misery to match a Category Five hurricane. When the impressively disintegrating Russotto stalks her with a pillow, brandishing it like a lethal weapon, it's funny only if you share his liberating joy in the use he dreams up for it. Here, it's not a delicious felony, only an expedient one.

Still, Cohen has constructed an entertaining, boundary-pushing comedy, a rebuke to bland sitcom writing, and Prewitt offers a shrewd assist with his pacing of the material. Although Anne Gibson's threadbare scenery is a tad depressing -- it smacks too much of the dreary set of "The Honeymooners" -- Michael Kraskin's sound design is a wonderful approximation of the sensory overload of New York.

Shalwitz, Woolly's longtime artistic director, is the chief attraction here. It's scary how marvelously this role suits him, how Lenny's depraved desperation can be made to seem so real, so tangible, so hilarious. Here's an actor to give malodorous parasitic bottom-feeding a good name.

Lenny & Lou, by Ian Cohen. Directed by Tom Prewitt. Sets, Anne Gibson; lighting, Adam Magazine; sound, Michael Kraskin; costumes, Debra Kim Sivigny; fight choreography, John Gurski; dialect coach, Christine Hirrel. Approximately 2 hours 25 minutes. Through Sept. 26 at Goldman Theater, D.C. Jewish Community Center, 1529 16th St. NW. Call 800-494-8497 or visit www.boxofficetickets.com.

Fran (Nancy Robinette) and son Lenny (Howard Shalwitz) in Woolly Mammoth's pleasing "Lenny & Lou."