I've been on a reality tv show once. The director told me exactly what to say and what to do. Not only that, but I was edited to look like a moron. Not my proudest moment to say the least. When I try to explain how editing works to most people, I get a blank stare.
BBC did a pretty amazing break down of all the work that goes into making a realty TV show star look funny, lovable or just plain crazy.