When you go in/out of water, put your thumb in the waistband and pull it open a few millilitres on the side ro let air out/in. No akwardly bloated or clung swim trunks.
Is this an American thing? Who's looking at your junk hoping to get a glimpse of shape under your shorts? Are you wearing shorts? You should cover up with your hands if you're not wearing shorts. Also, stop looking at your friend's crotches when they get out of the water. It's weird.