Some bad ideas have the decency to be entertaining, while others simply keep driving until the credits roll. That distinction is crucial to enjoying *Dude, Where’s My Car?*, a scattershot comedy that occasionally stumbles into genuine absurdity but spends far too much time mistaking immature behavior for clever writing. The movie’s biggest asset is easily the chemistry between Ashton Kutcher and Seann William Scott. Given the material, they make a surprisingly effective pair, selling the blank-eyed confusion of two stoner buddies trying to piece together a night they cannot remember.…