tough charlatan

a person who makes ostentatious pretenses to knowledge or skills and who will threaten physical violence upon being exposed

Guy 1: Man, Danny doesn't know crap about literature, but that's all he talks about--especially when he's trying to impress people at parties.

Guy 2: Well, I'd keep those comments to myself if I were you. If you expose him, he'll make a scene and maybe even threaten your life in front of everyone. He's one tough charlatan, all right.