A character in a movie/show who is only there to ask dumb questions and be a lazy plot device. They are either incredulous about the events around them, or stupid and can't sort it themselves.
'The characters in "Transformers" don't do anything, they just sit around and blurt out stupcredulous reactions to everything."
Tom: Oh man, Jim, I was heading to school today and I saw a BUNCH of retarded kids walking to their special school.
Teacher: Thomas Joseph Wilkins! You know not to use such language in the classroom!
Tom: Sorry, Mrs. Peterson. What happened was I saw a bunch of it started kids on the way to school. They were so it started that I went up and stole a bunch of money from each of them and they didn't even notice, and then I pushed one of them over, laughed at him, and yelled "get out of the way, it start!"
Teacher: That's much better Thomas.