A. An insult to say that you are unusually strange.
B. Someone who you should fear because of his or her physical power; or more specifically, someone who has a purple belt in karate.
both versions derive from Dwight Schrute from The Office.
Carlson: Eugene, did you just see that guy eat that worm?
Eugene: Dude, he is such a Dwight.
Rafael: Maxene! I could crush you into a million pieces, just as I have crushed this brick.
Maxene: Rafael, don't be such a Dwight. You're scarying me!