I think we all know someone like this.

pervicacious (per·vi·ca·cious): / pur vi KAY shuhs /
adjective

(1) extremely willful; refusing to change one’s behavior, ideas, etc.; obstinate; stubborn; headstrong

[From Latin pervicac-, stem of pervicax meaning “stubborn, headstrong, willful,” from pervic-, root of pervincere meaning “to maintain one’s opinion, carry one’s point,” from per- (“thoroughly, through”) + vincere (“to prevail against, conquer”).]

Usage: He was a bully if ever there was one, a pervicacious brute whose only importance could be found temporarily through the maltreatment of those weaker than him.