shifty cunt

Someone who is pretending to be your friend but who will turn you in for his own good by any chance at any given time.
In other words a backstabber, a rat or a snitch.

My work mate ask me to go have drink with him tonight to talk about problems he has with the boss and the company.
Due to similar problems I agreed and did have a drink and a pretty good chat with him that night, but the very next day I got fired because that shifty cunt told the boss all of what I told him last night.
Now he moved up to my previous position.