SpeedoGuy: Straight guy here.
I haven't discussed my size (or penis size in general) with very many friends. Of the few that I have discussed it with, though, they have been with both male buddies and female platonic friends.
Interestingly enough, its been those conversations about my size with the platonic female friends that I remember most vividly. I'm not sure why. Maybe its because I didn't initiate the topic of sex or size, but it still came up and, given the opportunity, I unabashedly participated in it.
At the time, they seemed to be just casual conversations where size came and went as a topic. I know it may not seem that penis size qualifies as "casual topic" of conversation but I didn't attach a heck of a lot of meaning to it at the time.
Looking back on it now, I can't deny that I found it very sexy when the topic deepened into a discussion of my own size. On a couple of occasions, the conversation partners were bold enough to query me directly about it and I didn't shy away from discussing it. Not bragging, mind you, but an open dialogue about the pros and cons(mainly pros) of being endowed better-than-average.
SG