It's a gym shower, not a bath house or glory hole. What the hell are you thinking? Sure, a lot of guys vigorously clean their dicks after their workout, but there's a big difference between a thorough scrubbing and what you were doing. You were fully erect, had the four fingers under/thumb over grip and were thrashing your junk like it was on fire. Have some fucking dignity and jerk off somewhere where that behavior is expected or at least close the fucking curtain.