Why Are Shemales So Funny?

Has anyone else noticed that Shemales seem to be the brunt of a lot of jokes. Possibly because people alway’s seem to find humor in things that they don’t understand or things that make them uneasy. This story idea came to me after Shemale Cocktail’s Tube added a ‘Funny’ category. While I have to admit a few of the video’s do make me laugh but they all seem to follow the same Stereotypical pattern… “Dude Oh my god is that a Tranny…Ha Ha Ha!”. So what is it that is EXACTLY that is so funny about a Tranny?