J.B.
I think it would be helpful if you could provide some examples of what he is saying because I can't tell from this whether or not he's being offensive or if you're somewhat repressed and view any talk of reproductive health as taboo. Excluding your children from health class is, frankly, an odd choice. There is no reason for both boys and girls to not understand the reproductive development of both themselves and the opposite gender. Ignorance = unexpected babies.
You say that you think this kind of education should be up to parents, yet admit that you're not sure that your 17-year-old knows anything about menstruation so clearly, you're NOT teaching this at home and you are letting your sons grow up ignorant of things that they should know about. If you're going to take on the responsibility of teaching your kids about sexual health, you have to actually, you know, TEACH them.
So. Either his comments are legitimately crude and unacceptable, or they're not and you're overreacting. In any case, he's clearly trying to get your attention and is behaving in ways that aren't typical for his age. He's acting very immature, but perhaps he's obsessed with this because instead of making it a normal part of health education, you've made it a big deal by avoiding it?
I would use this as an opportunity to sit down with him and have a frank talk. Call him on this: "hey, you seem to pay a lot of attention to menstruation and it occurs to me that dad and I never really talked openly about the health class content that we didn't allow you to learn in school. So let's change that and make sure that you know what you need to know. Because if you keep talking about it crudely and immaturely, I'm going to assume it's because you have questions or are curious and don't know how to ask question, and that's on dad & me, because of course this is awkward and you're not going to ask questions. So, here we go..." and talk, and talk, and listen and talk.
Then wrap up by letting him know that if he continues to act like a clown about this, you'll assume he's too immature for the rest of his 14-year-old life and will treat him accordingly...no phone, limited computer access, no un-chaperoned social events, no T- or M-rated video games, etc. Give him a chance to learn (and please fill your 17 year old in while you're at it), then be firm that acting juvenile about this or any other aspect of sexual health will relegate him to being treated like a 10 year old until he can learn to control himself and get over it.