Funny is funny, and 20 years of "America's Funniest Home Videos" and a decade of "Jackass" proves it. A shot to the groin is as reliable a laugh as there is. And if the shot comes from a baseball on a tee, a football place-kicked or a ram, bull or buffalo aiming for a man's center of gravity, so much the funnier.

"Jackass 3-D" fires paintballs and dildos right into our faces and gives three full dimensions to projectile vomiting and the after-effects of a heavy dose of laxatives. Yeah, they run out of really interesting things to do to each other pretty quickly, and out of things that look cool in 3-D pretty much after the opening credits. But they're still here, suffering for their art. Now it's our turn.

A mix of stunts gone awry, sketches and sophomoric gross-outs, "Jackass 3-D" can be as simple and stupid as having a dog bite Johnny Knoxville on the rump or having a Lamborghini pull a willing subject's tooth. And it can be as elaborate as Bee Hive Tether Ball -- scantily clad grown men swatting a hive around a tether ball pole, collecting stings as they do.

The funniest line from the TV show and all three movies is never "Hi, I'm Johnny Knoxville and this is Electric Avenue" (a stun-gun obstacle course). It's the opening disclaimer -- that these stunts are "performed by professionals." That's what makes them funny. They're not professional anything.

The sketches are what work best in this film. A staged dwarf brawl surprises unsuspecting bar patrons with a Little People love triangle, then a fight, dwarf cops coming in to break it up, dwarf paramedics arriving the haul out the injured. Knoxville dons convincing old age makeup to do assorted "bad grandpa" gags with his scooter, his sexual tastes and his bowel movements.

But those Jackasses from "Jackass" aren't getting better, they're getting older. Their teeth have all been fixed. Their growing paunches just mean more territory to cover with tattoos. A lot of what was cute when they were comic losers willing to try anything for a laugh a decade ago can seem a little desperate now. The peals of laughter by Knoxville, Steve-O, Bam Margera and their motley crew can feel forced, like the sidekicks on a radio "Morning Zoo," cackling at the boss's limp jokes.

It's faintly amusing to see Knoxville trampled underfoot when he roller-skates in a buffalo herd, though the sight gag isn't quite as funny as the Roger Miller tune that accompanies it.

And this fixation on feces isn't juvenile. It's infantile, puerile and gag-inducing. Cast members and a cameraman lose their lunch in this one, not exactly comic paydirt.

At least with every expected pratfall, somebody in that large ensemble -- from the blimp-sized Preston Lacy to the Wee Man -- has the presence of mind to ask, "What did you think would happen?"