Though Jim Parsons has collected tons of hardware for his performance as Sheldon on The Big Bang Theory, the character has one of the least consistent biographies on television. His charcter totally mutates based on the needs of the joke at hand. Sheldon makes sarcastic remarks, but yet "doesn't understand" sarcasm. It is mentioned that he is allergic to cats, but that he bought 25 cats after a bad break-up. He claims that hates physical contact, but is then seen hugging and even cuddling with other characters.
In season three, Sheldon claims he doesn't dance, but the next season he is an excellent dancer. There are more, but listing them all would be about as exhausting as watching The Big Bang Theory.