Help me come up with some good debate put-downs!!

My friend and I have a ridiculously easy class presentation to make for a class at college. We decided instead of doing a boring, normal presentation, we would take opposing sides and exchange intellectual barbs as we speak.

What are some good put downs I can throw at him during my portion of the debate? Ideally, they would focus on his brains and his ideas.

My best one is this:

My friend, you have the intellectual capacity of a tube of toothpaste.

By the way, keep 'em clean but cruel.