NEW YORK (CNS) -- There's a social document of a sort tucked inside the otherwise hopelessly juvenile "Jackass Presents: Bad Grandpa" (Paramount). Despite coming out of the titular MTV franchise -- in which reckless stunts are performed by people who are pretty obviously under the influence of banned substances -- "Bad Grandpa" is surprisingly amiable, and also respectful of its setting. Granted, considerable editing goes into a project like this. All the same, the film manages to portray the swath of red-state America between Lincoln, Neb., and Raleigh, N.C., as filled with chunky people who are kind, polite, indulgent to 8-year-old boys and to a leering comedian (Johnny Knoxville) made up as an 86-year-old grandfather.