John Goodman’s wry charm has something to do with the fact that his personality is so much smaller than his body. You’d expect a man who’s this huge — and in the past couple of years, he has gotten even rounder — to have an outsize, aggressive disposition, rather like that of his TV costar Roseanne Barr. Instead, Goodman is miraculously genial. In King Ralph, he plays a Las Vegas lounge singer who becomes the king of England when the entire royal family is killed in a freak accident. (Though American, he’s the closest blood relative they can find.) All of a sudden, he’s in pig heaven. The movie is an eminently forgettable string of bull-in-a-china-shop gags: Ralph hits a homer with his cricket bat, he sits in the royal bath wearing his Imperial margarine crown and scarfing Milk Duds, he does a genuinely rousing rendition of ”Good Golly Miss Molly” during a dignified ball. Like Kindergarten Cop, this is a high-concept comedy in which the gags seem to have been designed primarily for use in the movie’s trailer. Comedy — that is to say, show-stopping, rib-tickling comedy — is based on surprise, and there isn’t a single gag here that pushes the envelope. Goodman, though, is such an ingratiating performer that you coast through the movie right along with him.