My group is all guys, none of whom are married, half of whom are single. As the DM, I'm sort of loathe to invite women to the game, simply because it does change the dynamic, and I like the dynamic just the way it is.
I got a nice little lesson in this just the other week. We couldn't play at our regular place, so we played at another player's house. His girlfriend was home, and she kept coming into the room and watching us play. Everytime she would walk into the room, the whole mood in the room would shift. It wasn't a subtle shift either. It was notably jarring.
Mostly because we're a pretty raunchy group, and the adventure I'm running deals with slavers a lot, and so my slave girl miniatures have been making frequent appearances, with much accompanying off-color comments. It's Dennis Mize's Slave Auction (so they're little naked slaves), and was given to me by one of my player's ex-girlfriends -- the same player whose house we were playing at. His girlfriend noted the minis on the table, and he started bad-mouthing me as immature and sexist for using them. Just turned instantly into a "Sensitive New Age Guy," trying to make himself look all enlightened and above it. I've had those minis (which again, his ex gave me) for years, he's been playing with me for years, first time he's ever mentioned it.
Another of my players, a Coastie who is also our group's only Republican, recognized what was going on with the hosting player, and went from his normal blue jokes into territory I found kind of offensive, mostly I think in an effort to drive the girlfriend from the room. It was just tense all around, and I didn't wnat to deal with it. I just wanted to play.
I've seen some people suggest that if it changes the dynamic, then
the DM just needs to "deal with" the "problem player" and help them "get over it." I would like to suggest instead that as a DM, my job is to run the freaking game, not to play therapist to my players and help them sort out their various personal issues.
I have never understood why some people think the DM is supposed to take such a patronizing and condescending position with his or her players as to be responsible for "slapping a bit of sense into a few of the boys/men" to quote one user. I've played with some asinine DMs, but never one so obnoxious as to think they had the right to "slap some sense" into their players with regards to entirely non-game issues like how they relate to women.
Also, it'd be nice if people could stop throwing out the "fat virgins living in basements" thing anytime anyone asserts a preference for "guy's night out" style gaming. That's a cheap shot.