I recall my health class teacher back in highschool posing the question "Can you contract a sexually transmitted disease via Oral sex?" and requested a show of hands for both yes and no answers, one girl kept her hand raised in opposition to the group, after he politely asked her why, she replied "isn't that when you watch two people having sex? you can't get sick that way." Uproarious laughter ensued, predominantly because she was a notorious slut. 
Also:

Also:
In the event that you aren't pulling our leg for the sake of irony, said video has not only already been mentioned in this thread, but you can see it about a dozen times in the form of user's replies to it as well. (First page - 11th post no less)Ellen of Kitten said:God damn, he's right. He does win the thread.believer258 said:Also, Fox news is the most ignorant thing I've ever seen, and I win this thread.SIGH!
OT: I'd say a youtube video that was posted on these forums (that I can't seem to find right now) that has the stereotype of "stupid Americans" right in its spotlight. A man interviews several americans, and asks them basic you-should-know-this questions, and we marvel in their ignorant responses. If you know the video, you should help me out, and post it.