That screencap reminds me of that scene in Butch Cassidy and the Sundance Kid when they realize that to escape their pursuers they have to jump off a huge cliff. Sundance gets all nervous and confesses he can't swim. Butch bursts out laughing and says, "Swim!? Hell, the fall will probably kill ya!"
I bet thats' what happened behind the scenes in BBM. Jake was nervous about doing a nude scene, and Heath said, "Hell, the fall will probably kill ya!"