Nudity as Comedy

When did nudity in movies stop being sexy and start being funny? I speak, of course, of scenes in this summer's films The Hangover, The Proposal, Bruno and The Ugly Truth (opening Friday) in which the anti-erotic nudity of Zach Galifianakis, Sandra Bullock, Ryan Reynolds, Sacha Baron Cohen and Katherine Heigl is played for laughs.

First time I noticed this was about six years ago in Something's Gotta Give in a scene where Jack Nicholson loses his way in Diane Keaton's house and startles his nekkid hostess in the hallway. (This, shortly after a scene where Nicholson, on pain meds, wanders down a hospital hallway with the back of his hospital gown open.) Then there was Sideways where the Naked Guy runs down the street trying to beat up Thomas Haden Church who had his way with Naked Guy's wife. Since then, the naked Greco-Roman wrestling between Borat and his videographer in Borat has been a high of low gross-out comedy.

Do the laughs come from the surprise of seeing man and woman parts not in the service of titillation? Or....? Your thoughts?