If the Weinstein brothers had hired Stephen Hawking to postulate a foolproof formula for filling movie theaters with young male viewers, the result would very likely look a lot like their latest installment in the 32-year-old Piranha franchise: Spring break plus Girls Gone Wild-style shoots divided by football-sized, flesh-eating fish equals good, old-fashioned, R-rated horror fun.

The 1978 original was produced by Roger Corman, directed by Joe Dante, scripted by John Sayles and intended as a low-budget rip-off of the megahit Jaws. The makers of this movie understand that the only name with which its target demo will be familiar is that of Steven Spielberg’s proto-summer blockbuster and wisely keep the related in-jokes coming. In the process, they endear themselves to an additional market: AARP members who were around to be scared out of the water back when Roy Scheider first closed the beaches of Amity.

Scheider, regrettably, wasn’t available for a cameo in Piranha 3D, but Richard Dreyfuss was, and appears in the opening scene as a retirement-age Matt Hooper reprising “Show Me the Way to Go Home” and doing a bit of fishing on Arizona’s Lake Victoria (played by real-life Lake Havasu). Wouldn’t you know it — a seismic disturbance creates an opening to a subterranean body of water, unleashing swarms of fanged prehistoric piranha. Having survived his long-ago encounter with the giant fish, Hooper falls victim to relatively little ones. He should have brought a bigger boat.

The officer in charge this time around is played by Elisabeth Shue. Just as Chief Brody was back in 1975, she finds herself forced to deal with the unpopular prospect of shutting down the town’s beaches at the height of a holiday season — in this case, spring break. So, rather than families and old men in funny caps, the hamlet is overrun with drunk frat boys and bikini-clad girls gyrating to the blasting beat of some MTV-type shoot, complete with wet-T-shirt contests. Little does Shue realize it for most of the movie, but she shares another dilemma with her Amity counterpart: Her children have chosen the worst possible time to spend the day on the water.

Steven McQueen (grandson of the late great) plays her eldest. He’s hired as a location scout by Jerry O’Connell, in the role of a Joe Francis-inspired sleazebag who makes videos of young women going wild — or, at any rate, going without their bikinis. French director Alexandre (High Tension) Aja fits more nudity into the film’s 82 minutes than I’ve encountered in the past 10 to 15 years, and he has a heyday combining it with the F/X gore reaped by the titular (so to speak) flesh eaters. The sight gags run the gamut from the make-you-laugh to the make-you-hurl. Aja’s film will go down in cinematic history for, if nothing else, offering the first 3-D underwater display of male frontal nudity in which the male involved didn’t need to be present for his closeup. Think the pool scene in Caddyshack as reimagined by Lorena Bobbitt. Ouch.

Oh, and, as a deputy, Ving Rhames has a priceless Snakes on a Plane moment when he reaches his breaking point, yanks the motor off the back of a boat and uses it to puree every living thing within wading distance. The movie is wall to wall with gratuitous, gruesome stuff like that, and it’s just great fun. Piranha 3D has everything you want in pull-out-the-stops B-movie baloney, and more. And by “more,” I mean its writers leave it wide open for an even crazier sequel. If half the team behind this film regroups for another fishing trip, I’ll be there.

Something tells me they’ll be biting.