These boys are not yet comfortable being naked around each other. They keep holding their hands over their privates. They're joking around cuz they feel awkward having no clothes on.
In middle school sports we all went through getting comfortable with stripping naked and showering together. I've often wondered who much adds to bringing a team together, either in sports or the military. In a non-sexual way you grow closer to the guys who you see naked and allow them to see you naked.
