Here's a thought...

With the recent heat wave, I have noticed a kind of fashion trend...well, I've seen it on two guys, but in completely different situations. I've noticed that some guys, when they're wearing a short sleeved shirt, they leave the second button from the top of the shirt undone which exposes more of the person's chest. I know its not because of a missing button, as the button is clearly on the shirt.

So the question is:
a) it is cooler to leave that second button undone?
b) it is the guy's version of a girl wearing a low cut top?
c) its fashionable?
d) they forgot to do up that button when they got up that morning?

Very puzzling.