I guess I'm an exceptional case.
I don't go out of my way to tell everyone I meet, but I don't hide it either. I guess it's because, ordinarily, I don't have too much to boast about. For example, I know I'm a relatively smart guy, but academia isn't something to go on long whims about. For those who ask, I usually offer what I've studied in college, where I hope to go; can't really "compare" smarts without coming off as an ass. (We've seen that stuff on here, even. Hell, I've been as much a party too to discussion threads in which the participants seem to bat back and forth at whomever takes the title of demonstrating the most knowledge on a particular topic.)
I'm not a jock. I'm not really a stud either. To be honest, don't have too much to brag on -- at least on a physical level -- and as I've mentioned before, having a big dick sort of evens out the playing field, you see? Though I don't really have a self-esteem issue to contend with, if I talk about my size... well... it seems to have a strange "universal" appeal, you know what I mean? Girls get pretty shocked; some guys turn envious and rude, but I usually get the affirmative nod / "That's cool" before anything else. As it goes, I don't really have a problem telling anybody -- in fact, it usually slips out one way or another, especially if conversation about sex come up. (I don't pawn off my measurements so specifically, but I usually say "as a well-endowed guy" or something like that.)
Maybe what I'm trying to say is, there's nothing wrong with being proud of what you've got so long as your personality or sense of humor doesn't fall by the wayside?