I think sometimes it's a matter of fashion. I'm regularly around a lot of women and their kids, and there is one in particular that has HUGE boobs but wears little summer type shirts that are clearly not made for her chest size. If anyone ever comments on her boobs, she seems genuinely surprised. Which is amazing to me.
I honestly don't think she does it for attention. She's not flirty and it's mainly all females when she's around. But it's hard not to stare when she's got GG size boobs stuffed into a tank top right in front of your face. It's very warm and humid where we live, so the clothing style here is mainly summer stuff. Sometimes she'll tell me how much she likes whatever shirt I'm wearing and ask me where I got it. I always think- "How in the hell do you think you're gonna get THOSE into a shirt like this???"
