jackface
A total idiot who thinks they're the smartest person in the room, but they're actually the dumbest.
"He's a jackface, and he thinks he's the king of the school.", said by a kid who was actually the king.
"That jackface thinks he's cool, but he's just annoying.", said by a kid who was actually cool.
"He's a jackface and he's still in my class.", said by a kid who was glad he was in the class.