Exactly, we should tell them directly. It's more effective, and it renders sweeping generalizations like the original post unnecessary. People need to be more direct. I'm not a confrontational guy, but I recall one time at a bar I was making polite conversation which by no measure suggested I was interested (like, talking about the weather or something while waiting in line for a drink) and the girl made some comment along the lines of "sorry, I don't hook up with guys I meet at bars" and I was pretty awestruck by her leap in thinking. So I told her directly, "Don't flatter yourself, honey". Definitely blunt, perhaps a little rude, but I'd like to think it made her reconsider her stupid behaviour. The same bluntness needs to be directed towards a lot of men.