I think if anything it's more like a 'finishing touch' before the reveal. Most tits look better with erect nipples, and it also implies sexual arousal.. so if a chick is taking her top off and showing you her boobs, it seems only natural to want to make 'em look their best. I don't think I'd call it being self-conscious though
BTW - Happy Birthday Jim! What a great way to spend your birthday; looking at boobies!
