Someone who, no matter what your argument or how you frame your beliefs/ideas will just not listen.
Basically someone who says, "Listen, I know I am right and if you try to change my
mind with facts and
logic I won't listen and I will consider you a
pos for even attempting to do so!"
Karen: How could you possibly
think that citing Wikipedia as a source is acceptable!
Guy: Okay Karen,
stop being such a fucking porker.