I've not seen 2007's Wild Hogs, nor do I really have any interest in doing so. I did however, find a clip of the skinny dipping scene. John C. McGinley play the Highway Patrolman looking for friendship. He briefly joins the traveling foursome, while they're skinning dipping, giving us a nice view of his meaty muffin. McGinley's character left alone in the lake, after closing his eyes for a game of Marco Polo.
One of the most interesting things about the scene isn't so much the scene itself, but some 'behind the scenes' shots of the actors that came out on a site entitled 'On location new's after the film was released. The shots showed many of the actor arriving on set, stripping down to their skin colored pouches and getting into the water.
Although all five actors in the scene were supposed to be naked, only McGinley and actor William H. Macy actually showed their butts. Not that anyone was really hoping to see Travolta's tushie or Tim Allen's ass. Given however, that young and fit actors are often ridiculed when doing nude kudos this group of actors who were brave for stripping off their shirts for the scene.
Whenever I've seen the 'behind the scenes' shots, the full frontal image (below) of McGinley usually makes an appearance. Although McGinley is seen in a modesty pouch in some shots, he also had to remove, or at least lower it, for some of the shots in the film. The shot may well be a fake, but there were also reports it's real and that the actor's pouch fell off while filming, and he simply decided to continue without it. Maybe someone will ask the actor in a future interview what the story really was...