Back stabber

[Britney]

Backstabber- Some one that you have grown to be really close friends with, but then they go and go behind your back and betray you.

[Justin Bieber]

A person who betrays a freind, like when Brutus stabbed Ceasar.

[Becky]

Someone who pretends to be your friend; but talks shit about u to other people
*** can also be said to be when 1 likes a boy and the friend knows that, and all of a sudden the friend likes the same person