The brain trust behind Jackass — director Jeff Tremaine and performer Johnny Knoxville — attempt to elevate the pranks-and-stunts-and-assorted-gross-outs franchise to pranks-and-stunts-and-assorted-gross-outs-PLUS-heartwarming. To that end, we get Bad Grandpa, where the assorted Jackass mayhem is incorporated into a larger story about a cranky senior citizen (Knoxville, made up as an oldster) tasked with ferrying his guileless grandson (Jackson Nicoll) across the country. Along the way, the pair enacts real-life hidden-camera pranks, many involving the use of prosthetic geriatric genitals. And somewhere between the beers and the exploding underpants, Grandpa learns a valuable lesson about family. It's an awkward mix that occasionally works, but Bad Grandpa's biggest failing is simply that heartwarming or vulgar, the material feels stale. (The film's big showpiece, in which the pair invades a kiddie beauty pageant, offers the same joke as Little Miss Sunshine, for Pete's sake.) Nonetheless, the screening audience roared its approval, and apparently, there's no limit to the laughs that can be wrung from one pair of fake old-guy balls.