File under "Peeves, Pet"

Sometimes if you ask a guy if he has kids, he'll answer "None that I know of." You can tell he's trying to be sort of clever, and at least theoretically he's being a stickler for accuracy, since technically only the mother can be 100% sure that a baby is hers.*

But when you think about it, what he's really saying is that he's had unprotected sex with at least one woman he didn't know well enough (or wasn't on good enough terms with) for her to be willing and able to contact him a few months later to notify him that she became pregnant.

fn*: Then again, in hospital environments, a mother cannot always be certain a baby is hers; one does hear of the occasional "switched at birth" story. In the U.S., they're often caught within hours... But this one was corrected 43 years later.