chewbaca was a sith!!
born on a sith planet, the inability to fix the hyperdrive in time before the falcon is pulled into the tracter beam, the laughing at han when he is getting tortured, and the chocking of lando, so that leia can not hear how to save han, and most of just being a sore looser at checkers.
p.s. boba fett was not nodding to boush, he was signaling to chewie.