Heh, funny story about the last bit-- when I was maybe 13, I was playing tennis with my older brother and my dad and being summer outside Baltimore, it was hot as hell. So my brother took off his shirt to play and without thinking, I said "Wish I could do that!"
My brother felt bad, so he put his shirt back on. Were I older/smarter, I would've said he didn't have to, I understand that it's just the way it is, but I still think it's sweet (particularly coming from a 21-year-old, which he was at the time).

My father, of course, being an Italian-American and quite hefty, was required by law to keep his shirt on. ;^)