Someone needs to burn this flowchart: Two mismatched and obnoxious people meet cute/drunk, are forced by a cranky judge to cohabitate, and then miraculous things happen in which they reveal unforeseen personality depths and fall in love. "What Happens in Vegas” is what happens when deeply cynical people get too familiar with that flowchart and make dull romantic comedies.

Jack Fuller ( Ashton Kutcher ) is a man-chi...