A Language Log post the other day included a use of the word boob by the male blogger, Victor Mair (whose always interesting posts have featured on this blog before):
sonar-like semi-circles emanating from the model's left boobWhile boob is of course in very common use, and is perhaps the most common word that I hear for these body parts (subjective statement alert), it sounds funny to me to hear a man use the word (not completely weird, just enough to notice).
Perhaps men talk less about boobs generally than women do (sounds unlikely, I know), and when they do they refer to them in a more formal manner with the more neutral, formal, breasts? (Unless it's a discussion of someone's merits or otherwise in that department, in which case it's often tits.) Discounting lads'-mag discussions and passing mentions, that leaves few occasions for a man to use such a familiar word.
(Disclaimer: My thoughts apply only to UK usage, of course, and pretty only much my own experience.)