Agree with the no eye contact. I'd probably start by saying, "I know you are a smart kid and I know you've learned stuff in school, but when it comes to sex, it's really important to me that you know: (1) what consent does and does not look like (like you can't have sex with a drunk/high girl/woman), and (2) some info you hear from friends and on the internet often is not true. You need to either ask a trusted adult, or here is a website that has correct information."
According to today's standards, I did everything "right" in terms of discussion sex ed with my son. We started early, around 6 or 7, we talked often, we have an open relationship where he feels he can tell me most things. I have always told him I would prefer he wait til he gets out of high school, but that it should also be in a healthy, monogamous, loving relationship.
Well, that didn't work and he had sex at 15 with the first girl at a party who asked him. And he later told me, "mom, you didn't cross my mind AT ALL." Which of course, makes sense, but dag, all those years of talking for nothing.
However, he did use protection, he did check on consent, so there's some evidence that discussions helped.
Some real life things that have come up with my son and his crowd this summer.
One boy was almost stalking a girl that he wanted to get with, despite her having a boyfriend. We discussed how completely inappropriate this is, how uncomfortable it makes the girl, and people will look down on my son for hanging out with this kid who was quickly developing a reputation for being a complete ass.
Another boy (not my son's crowd) has been accused of sex assault. Not to the level of police involvement, but rumors around school.
Your son needs to know this goes on. That things can go sideways fast, not necessarily for him but for friends, and he needs to know he can come to you with anything.