I was working late one day and a "dumb" co-worker and another co-worker who work later than me were both there. "Dumb" co-worker was a few feet from me and the other co-worker didn't know I was working late that day. So she comes out of the break room and says "Oh, Team Manager, you're still here?"
I jokingly say "No, I left!"

Honest to god, "dumb" co-worker jumps out of her seat and says "HE'S LYING, HE'S STILL HERE."