Why do men take off their shirts to fight?

Canada
@whywiki (6079)
May 12, 2008 1:14pm CST
I am cruising down the street late Saturday night checking out the action. I see a group of three men(boys actually in my opinion)and they are yelling down the street at a couple. The guy is shirtless and yelling at his girlfriend that it was her fault he got into a fight. I wondered to myself what goes through a man's head before he fights. Is it oh I should take off my shirt so I don't get it covered in blood or ripped. Or is it look at me aren't I hot? I thought it was the shirt getting ruined that make guys take off the shirt before the fight. Hubby says it is because they are posers. I tend to agree with him when I think about it. Have you noticed guys doing this and why do you think they do it?