Better oblivious than a horn dog, I say. And I agree that being oblivious to flirting doesn't mean he doesn't know about sex. I know about sex but if someone was flirting with me, I wouldn't pick up on it (in part because it pretty much never happens). But really, why are you so eager to get your son laid, and with a random woman? Let him do his own thing.

Oy vey, that's sad.

Maybe she was hot to your older eyes, but to a 20 year old she was not all that.

well, to me son seems more mature than the father.

I think you need to do some introspection, OP. Your son might be straight, but not interested in this woman or one night stands. He might be gay and not interested in women at all. He might be assexual and not interested in anyone sexually. Or maybe none of these are true and he just didn't feel comfortable accepting it in front of you or in that setting. Even if he is straight and interested in flings and was just oblivious to her flirting, there is nothing wrong with that. Please accept your son as he is. As long as he's kind, polite and law-abiding you have NOT failed as a father.

To be fair, I was equally oblivious to women at that age. I had ladies behaving similarly and their advances went entirely over my head. Things kind of clicked when I got my first boyfriend though.

Or he was ignoring her flirting because he wasn't interested.

You haven't failed. You've succeeded.

He's 20, I think he can handle himself.

Some guys have all the luck with women but too dumb to realize it. You didn't fail as a father op I think your son is just slow when it comes to women.