I would love to take offense to that but honestly it is a little bit true so... A lot of the guys I see doing douche bag things at the gym tend to be wearing as little clothes as possible. It is the extroverted nature that makes them dress that way, not being a douche. However being an extrovert and a douche at the same time is like handing a douche bag a megaphone. You just can't miss them.
On the same note a lot of the guys in the sweats and hoodies seem to be d!ckheads. However not all of them. Same with this scenario.
It is funny, I used to pick my shirts based on how well they showed of my physique, now I pick them by trying to make sure I don't look like my only goal is to do so. Once I got to a certain point trying to display my physique in street clothes became a douchy thing to do because no matter what shirt you put on this amount of muscle can be seen. When you resort to stealing clothes from your 6th grader to show off you just look like a moron.