Dad: No, they couldn't.
Son: Yes, they could because mosquitos suck blood. There's no reason
why vampires couldn't have evolved to suck blood and... [long
explanation about how vampires might have evolved alongside humans].
Dad: OK, but the real questions is, "Do vampires produce sperm?
Son: What? I don't know.
Dad: I mean, "How do vampires reproduce?"
Son: By biting people's necks.
Dad: That seems pretty effective to me. Don't you think evolution
would have concentrated on that and pretty much done away with sperm?
Son: Dad!
David: I'm just saying that if vampires did exist, they wouldn't be
going around making out with high-school girls because they wouldn't
have the balls.
Son: You're embarrassing me.
Dad: Sorry.