A Derek is a person who thinks he is right all the time. He has absolutely no friends. He tries to act and sound tough by yelling at everyone and trying to make them feel stupid, but if push comes to shove he will ALWAYS back down. He will never admit when he is wrong and will never apologize for something he has done, no matter how wrong that thing was. He will try to make himself seem like he is always right and play it off as nothing when he is proven wrong. He will even try to turn his own wrongness against the one who proves it. He is a pathetic excuse for a human being.
The Derek: "Shut up! You're wrong! You're stupid!"
You: *punch him*
The Derek: *hides in the corner and cries*
The Derek: *complains about it behind your back*
"He acts like he knows everything."
"Oh, yeah. He's a total Derek."