A Sean

A Sean is an eldritch witch that kicks your butt as a dungeon master who then promptly teaches you how to handle other peoples idiocy whilst building a house with his army of goons

Friend 1: This eldritch witch just kicked my butt as a dungeon master and then taught me how to handle other peoples idiocy while he was building a house with his army of goons, it was so bizarre
Friend 2: Oh, don't worry about that, that's just A Sean! A Sean doesn't do any harm, they're kinda fun, too.