Term used to describe someone who gives away information about someone. An informer or snitch. This person is generally a bit of a loser, is incredibly boring and ugly, has a ginger beard, receding hairline and smells of poo.
That guy is such a Xander! He told everyone about the time I was having a bit of innocent fun in the hot tub and deliberately exaggerated the situation in order to try and get me in trouble.