A co-worker that lures you in to thinking that mediocrity is commonplace at the office. Just when you think you are both on the same page he or she will make look bad by putting together elite spreadsheets, cutting edge PowerPoints, and insightful talking points at meetings.
John: Where is Lindsay? She normally takes a 2 hour lunch with us?
Jim: Oh you didn't know? Turns out she is a closet overachiever.