Jackweasel
A person who is so clueless, they think they're the king of the world. They don't know what they're doing, and they don't care.
My math teacher is a jackweasel. He failed me for no reason.
My friend’s dad is a jackweasel. He called the principal a dummy.
My cat is a jackweasel. He knocked over my cereal and didn’t even apologize.