Gym dick is a result of enduring marathon days inside of a gymnasium for a wrestling tournament or similar event. The dick becomes listless and withdrawn, and no amount of staring at members of the opposite sex can revive it. You know you have gym dick when you go to the bathroom and the dick has recoiled, becoming wrinkled, clammy, and possibly tucked into its own sack.
Guy 1: I'm worried. When I went the bathroom the 12th time today, I couldn't find my dick. Then I found it, but I couldn't stretch it far enough to pull it out of my zipper. I finally had to go to a stall and piss with my pants around my ankles.