A Shifty is a person that thinks he's the best, blames other people for his mistakes and doesn't understand that people do not always have time for him of things he's busy with. He generally gets mad at the people he doesn't understand.
Me: Hey, I can't make it tonight, sorry. (For let's say: Battlefield clan war)
Shifty: Then just don't come back idiot, we don't even need you anyways.
Friend: Why does he have to be such a Shifty?