Workemy

A co-worker who appears to be your friend and confidant, but is really sabotaging you at work behind your back for career advancement.

Where is Shelia? I thought she was going out with us tonight.

Nope, she turned out to be a workemy.

What is a workemy?

You know, like a frenemy, but at work. They are all buddy- buddy with you, but behind your back are screwing you over to get ahead on the job.