Jacaiden
Someone who thinks they're smarter than they are and acts like they're the boss of everyone, all while having a brain the size of a pebble and a bump on their skull.
Post: "My teacher is a Jacaiden. She failed me for no reason."
Message: "He got in trouble for throwing a pencil. Classic Jacaiden."
Comment: "My cousin is a Jacaiden. He yells at the mailman."