Four

Although Four seems to be calm most of the time, he does get angry in "Lick Your Way to Freedom", "Why Would You Do This on a Swingset", "Fortunate Ben", and "Four Goes Too Far". Four was well-mannered in "X Finds Out His Value", however, and didn't screech. But in BFB, he has a mysterious, sadistic personality where he uses his powers to harm the contestants just for its fun.