It offends my delicate sensibilities :wink:
Seriously, I don't have a good reason, it's just a personal preference - perhaps it's something buried in my subconscious from the way I was brought up. I don't know. I know that I don't particularly like going round without a top on, and don't like seeing other men (or women if they so choose for that matter) doing the same.
For example, if I go to the beach or lake or whatever to go swimming, I'll always put a t-shirt on when I'm not swimming. Don't know why, just do - helps me stop getting sunburnt as well.
You'll never see me in a nudist colony!