Chair Cookie

Someone who contributes absolutely nothing to the world around them but merely sits there.

Student 1: Moe is such a chair cookie!
Student 2: Don't be so harsh. He got a 14 on that last math quiz!
Student 1: Yeah, but the teacher said she'd give us 14 free points for turning it in!
Student 2: Well, at least he turned it in.
Student 1: Actually, I found it on the floor and handed it in for him.

Student 2: Chair cookie.