Wow, seems like I really have an unpopular opinion with this. Didn't know that.
I think it is fine if you take your shirt off in the summer, when it is really hot out and you're sweaty. But I got the impresion that a lot of skaters take the shirt off the minute they step on their skateboard and to me that seems jockish.
Maybe there are so many fat people around that you want to show off, when you're athletic but this body cult thing is annyoing.