Actor-screenwriter Simon Pegg’s follow-up to the surprise hits Shaun of the Dead and Hot Fuzz isn’t as quirky or distinctive as those earlier films, but it confirms he’s one of the only comic actors working today who’s as adept at banana-peel pratfalls as he is at delivering brainy verbal wit. Pegg’s Dennis has never lived down the day, five years earlier, when he made a feverish 500-yard dash away from the altar—and his pregnant bride, played by the exquisite if overqualified Thandie Newton. The weight of that decision bears literally on him: He’s now a paunchy watchman at a posh lingerie shop. When his still-smarting ex takes up with an overachieving fitness nut (Hank Azaria, oozing self-satisfied smarm), Dennis wakes from his ever-say-die funk to declare he’ll run the same upcoming marathon as Mr. Right—in three weeks’ time. What flab Run, Fat Boy, Run has comes from the adipose prefab elements it’s lifted from inspirational sports sagas and romantic-comedy clichés: As director, actor David Schwimmer doesn’t supply the sixth-sense timing or jittery visual panache that Pegg gets from his usual collaborator, Edgar Wright, which stifles the sight gags. But Pegg has staked out a peculiar slant on genre material that ventures beyond irony toward rehabilitation. And nobody plays blithe humiliation with more style.