Hey, guess what? You need sperm? I can help you out! Haha!
Apparently men get off, so to speak, on talking about their sperm. It's not enough to talk about sex all the time, or about lesbian sex, given the opportunity. Guys have to reinforce that they are not only into sex, but into fertilization, too.
What the fuck? Men have an inordinate number of lesbian fantasies, and I have seen the porn. (Not all of it-- although there are a couple guys I know who might have.) I've always assumed they got turned on at the idea of women so sex-crazed they would even do it with each other, or that it was a power-trip to get a woman who didn't want men to have sex with one anyway. I've never asked, though, because I know that would delight the man even more.
What definitely delights men is reminding us that they have sperm. Yep, they've got it. Don't bother buying it, ladies: they've got your semen right here.
Is this about masturbating? They want to talk about jerking off? Um, hot, dude. Tell me more about how you're so ready to fill a cup for me.
Undoubtedly there are evolutionary imperatives manifesting themselves. Friends, co-workers, other friends and co-workers... they all want to alert us to their fertility. Not to take advantage of an easy cliche, but the New York Times says monkeys do, too: they tote their fresh-birthed offspring around, not 'cause they like them, but to let other male monkeys know that they've reproduced.
But that's fucked up, guys. Put the porn aside and go inseminate a woman you've met-- in person!-- and persuade her to carry your child. Don't rely on us dykes to get you off and spread your seed.