He/She in New Horror Spoof

by Debbie
(Spencer, WV. USA)

So, I was watching T.V. and a advertisement for a new comedy/horror spoof came on. In it there is mention of a movie that I can clearly remember seeing as a child.

I don't remember a whole lot about it, but basically there is a camp of some kind and a girl there is killing everyone... but it isn't actually a girl. It shows at the end of the movie the person you thought was a girl standing up and raising her hands in the air and you get a full on frontal of his penis and that's when you find out that it's a dude.

I know it's very vague and I don't have a lot to go on... but if anyone could help me it would be great.