I've yet to meet a straight woman who really thought that, luckily. But I have known plenty that thought they were going to get their boy to "change" in some kind of drastic way. (Of course, to the woman involved, it wasn't all that drastic--it's just the way the guy has been since birth.)

This also goes for all of those guys who are convinced that every gay man wants to hit on them. I heard WAY too many times growing up: "I'm ok with gays as long as they don't try to hit on me," usually from hairy, smelly, severely overweight redneck guys.