I would also have been really irritated. First, that she brought her boyfriend to a girls-only lunch; and second, that he was such a boor while he was there. If I knew and liked both the friend and the boyfriend, I might have made a joking remark like, "Ken, what are you
doing here? This is supposed to be girls-only, you know!
But, perhaps oddly, I don't think I would have done that if the guy was a jerk, because it would have been too pointed, you know? I think it would have been a very awkward lunch, and sadly I would've tried to end it as early as possible, just to avoid being around the boor. Then I think I would've scheduled something with JUST C, who at that point would probably not bother to suggest including K again. With two small kids the second gathering might've had to be at my house or something like that, less than ideal for carefree conversation, unfortunately.
Would I say something to K... Ergh, I'm very non-confrontational, myself. If we were attempting to schedule another girls-only event, I might say to her, in a light-hearted way, "Remember, this is girls-only! You can leave Ken at home this time, we don't want to bore him again! Ha ha!" If Ken kept popping up even when he wasn't invited, sadly I would just stop inviting K to things, or going to intimate things she was invited to. I mean, if she asked I could tell her it was because of Ken, but honestly I don't think I personally would volunteer that info. I think there are polite ways it could be said, though.