I have a few friends who are pretty curious about this show, as it's one of my favorites. However, my friends might not be able to handle some explicit stuff, and I haven't seen it in a while. Anything that you know of that would bypass the US pg-13 standard? I am aware of the cursing, but any sexual content that I may have missed?
If your friends are at all likely to be offended by sexual content beyond a US MPAA PG-13 rating, you should not show them MM. Memor-X points out in the comments that Right-Stuf lists the show as 17+ and Sentai Filmworks rates it TV-MA, and it's not hard to see why. This is a show about a masochist who derives pleasure from being tormented by beautiful women. Many of the other characters also have fetishes and tics that go beyond what you would see in an MPAA PG-13: there's a sadist, a voyeur, a lolicon, an aggressive quasi-rapey lesbian, a transvestite, and the main character's mother and sister, who both fantasize about being romantically involved with him despite being related by blood. And if that's too subtle, there's plenty of nudity, aroused moaning, and other sexually suggestive imagery, pretty much all of it involving underage characters. (Not drastically underage; the main characters are all in high school, so they're around 16. It's not exactly child porn. But it is yet another reason why I wouldn't show this series to just anyone. And Mio and Noa both look young.)
Ask yourself if you want to sit there with your friends while they watch a girl hold another girl helpless and grope and strip her as she blushes and moans, saying things like "Tell me you like it. You like it, don't you?" Ask yourself if you want to have to explain to them why the main character's sister just stripped down to her panties and jumped on top of him. Think about how much you would relish the looks on their faces when they find out what a lolicon is.
It's easy for we fans to get used to these things and forget that it's shocking for a lot of people. It might just seem like wacky fun to us, but to a normal American, this is some screwed up abnormal stuff. Unless your friends are already hardcore otaku who eat this stuff for breakfast (not people who've been into Naruto for years and recently watched Attack on Titan), I would just stop even mentioning this show. Don't show it to them. If you think they might be open to this kind of sexual free-for-all but you're not sure, show them something like Love Hina or maybe To-Love-Ru first just to gauge their reaction.