After I taught a round of sex ed last Fall, I've been using the curriculum I developed to talk to the freshman (who only receive sex ed once a week during PE). Another teacher and I split our two advisories into boys and girls and have single-gender talks; I take the boys (we tried the opposite arrangement one week, but it led to crickets for me and chaos for her).
In my sex talks, I try to front-load the awkwardness and get it out of the way. I give my little speech: "For the next few minutes, I expect you to act like adults, and I'm going to talk to you like adults. If anyone feels uncomfortable, they are free to leave at any time. So if you can't handle me saying words like 'penis', 'vagina', and 'orgasm', I suggest you get out." Here the class giggles, then chew one another out for giggling -- "Hey man, are you not mature enough?" -- and, usually, we're ready to proceed, giggle free.
I answer any and all questions. I have fielded queries on topics as diverse as the location of the clitoris, the disputed existence of the G-spot, the cause of "morning wood," the evolutionary utility of female orgasm (or lack thereof), the cross-species rates of homosexuality, and so on. As long as students aren't being deliberately vulgar, sexist, or homophobic, then I'll answer it all.
I think it's important that, in this very closed-mouth community, these young men have a male figure who they feel that they can come to with questions. Plus I get to push my radical gay-people-aren't-going-to-hell-and-it's-not-okay-to-beat-women agenda.
Naturally, I get some interesting questions:
"So... the man is always on top, right?"
Student: "Uh... Mister? Do girls always have camel toe?"
Me: [thinking that he is referring to the fashion faux-pas] "You mean, do all girls... wear their pants too high?"
Student: "No I mean... the shape. Is it always shaped like that down there?"
Me: "You're asking if all girls have labia?"
Me: "Then yeah."
Student [raises hand]
Me: "Yes, Jose?"
Student: "Hey Mister, I totally nutted on a girl's face one time!"
Me: "It's time to leave the room, Jose."
Me: "..so developmentally, the default path is female. All fetuses start out that way..."
Male Student: "So... boys start out as girls?"
Me: "Yes, you can think of it that way."
Male Student [turning to neighbor, also male]: "Ha! You totally used to be a girl, man!"
Female student: "Mr. N, is it bad when your vagina bleeds?"
Me: "Sure you want to ask this in front of the class?"
Female student: "Oh, not me! It's my friend's vagina."