Jeff Tremaine’s hidden camera road trip comedy Bad Grandpa (C-) offers Johnny Knoxville in full makeup as a cantankerous codger and child actor Jackson Nicoll as his sidekick and prank co-conspirator in a threadbare plot about delivering the boy from jailbird mom to even worse dad for custody. Knoxville is game for the highjinks but fails in adding any authenticity to his character, which means Nicoll carries most of the film’s minor charms on his small but mighty shoulders. The highlight is the film’s finale, an infiltration of a kid beauty pageant, and even that joke has been done before in Little Miss Sunshine. Still, as a prank and gag-filled throwaway endeavor, it’s got some occasional sweetness. The end credit bloopers make it look incredibly fun to make, even if that fun only intermittently manifests onscreen.