Clue-Brick

When a person really needs to get a clue, but he is so dense and/or stubborn that the only way he would get it (i.e. comprehend) is if the clue was launched directly at his head via a brick.

"It doesn't matter how much you argue with that guy, he's such a Neanderthal it would take a clue-brick to even get through to him. DUH!!"