Also, have you lately been to a students' club? In some places (and not even of the lowest quality) kissing and proposing sex to people you barely know is pretty much a normal behaviour. (this happens from both genders)
Now you have lots of people coming out of that environment and expect them to figure out by themselves that this is a different environment? Of course there will be someone who doesn't quite get it.
It also doesn't help when in some environments women are ok with as much attention as they can get. I've seen a couple of IRC channels of open-source projects where there's a regular female user appearing there. Strictly no-offtopic channels suddenly switch to 2h "what's new in your life in any details you want" discussions between her and 10 random guys that includes innuendos every once in a while. Again - do you expect those people to figure out themselves that it's not the same environment?
I really don't think this is a problem "of open source conferences". It might be something that manifests there more often than in other places.