Four junior wiseguys trying to prove themselves set out for cowpoke country to retrieve a big bag of misplaced money. Can't you just picture the sleeping-with-the-fishes-out-of-water yuks? Surprise: ''Knockaround Guys'' plays the premise straight, toying with familiar Mob themes of honor and betrayal while coming to a very slow boil. What keeps it (barely) watchable are Pepper's moody intensity as the conflicted son of the big boss (Dennis Hopper), Diesel's brawny cool as a low-level enforcer, and John Malkovich's glazed hamminess as an old-school Brooklyn mobster. Whenever he's on screen, the movie is sorta funny.