A man turned to a young woman near him and asked, "So, do you actually read Less Wrong, or did someone drag you here?" I asked, "Are you saying that because she's wearing heels and lipstick?" "No, no," he answered, flustered. "It's not because of how she's dressed. It's just that most of the women who come here are dragged by someone else." I asked, "Do you think that any woman, no matter why she came here, would feel welcomed by being asked that question?" At that point he began apologizing, and the other woman assured him she wasn't offended.

Whether the man was being rude depends on the details of the context. Specifically, the attitudes and personality of the recipient, how well he has inferred them and how he presents.

Whether the interloper is being unpleasant is far less ambiguous. Butting in on conversations and throwing about social political opinions is, all else being equal, an obnoxious behavior. If one of those involved is in fact offended or can reasonably be expected to be then it may be tolerable or outright welcomed. However if both participants were content with the conversation and made uncomfortable by the interjection then they would quite rightly update in the direction of the interloper being unpleasant to be around.

(FYI: I don't recommend that particular conversation starter. It is a little clumsy and that kind of self deprecation can backfire.)