I have a problem about this

It is because, it was someones suit in his family named Doug.

well dean is his real name is dean but some one calls him doug

I don't think it's ever explained. My guess is that it isn't his shirt. I also think he has one that says Peter... I don't know, I can't for the life of my remember the episode! Maybe I imagined it, huh.

on each of his shirts or shorts it says a random name, and i think its really wierd. why cant have his own name on his shirts and pants

It's on it suits

alex will win i hope she win i love you alex