A creature who displays characteristics that include stupidity and ignorance of the situation and setting that they are in.
John: Wow that cow doesn't seem to do much, but eat grass. Hmmm, a cow that just eats grass.
Al: Yes John, that type of bovine is called a maddnism.
John: Why? Is that a good thing?
Al: No, John that is a bad thing.
John: Oh, like a half back trying to tackle his quarterback, or me commentating games.
Al: Yes John.