I think there's a healthy balance between feeling proud and expressive about having a big dick, and just plain being an ass about it. I've made mention of my size before with my friends. If they thought I was bullshitting, I would prove my claim without a problem, and of course they'd react to it. I'd laugh it off. Maybe it's because, somehow, I don't look like someone who would have a big dick, whatever prototype that would resemble.
Then there are people like Jonah Falcon who are clearly fixated on their size, to the point that it drives people away.
Naturally, I think women are hip and cool enough to appreciate size and even to be bold enough to talk about it without getting all flustered. Some just don't have that Puritanical drive that equates big size talk with evil morality. You just have to "feel" the woman in question out; she'll let you know with her body language, her postures, and her conversation if she's comfortable with her (and your) sexuality or not. If she is, go for it. Don't be a clod and whip it out on the table. If you get into sex talk, bring it up then.