Las Vegas is the quickie wedding capital of the world, a city synonymous with winning and losing bets, both at the tables and at the altar. Tying the knot, Vegas-style, usually connotes images of inebriated couples, Elvis-impersonating pastors, and the kind of bad judgment your mama always warned you about. No wonder Sin City nuptials are such a favorite subject for screwball romantic comedies. The latest, What Happens in Vegas, starring Ashton Kutcher and Cameron Diaz, joins a pantheon of memorable — and regrettable — wedding flick pictures that have improbable couples uniting in the unholiest of matrimonies.