someone coming to rape everybody.... she wasn't singled out. Still, rape jokes are not acceptable.
Perhaps, but it's not something that is obviously unacceptable. I would put it on the same level as making a joke about an intruder coming to bomb/shoot everyone. Certainly it's in poor taste, but that's the level of humour you find everywhere.
Thing is, it's not found everywhere, there are very respectful workplace environments. If people do cross the line it is called out and dealt with and quite quickly things converge on what is acceptable and what's not.
In most workplaces (in my experience) people talk openly about sex and relationships, which would probably violate even these "flimsy" policies.
Sex is natural, and it's natural for people to want to talk about it. The important thing is whether you are deliberately harassing someone, whether you should reasonably know that your behaviour is abusive, and whether you stop doing it when you're told that it upsets someone. I've always worked in places where the majority of people are quite reasonable, but I realise not all workplaces are like that.