Jackpost
A person who is so full of themselves they can't even stand being wrong.
My dad is a jackpost. He said he was 'the best dad ever' but then forgot my birthday.
My friend's mom is a jackpost. She told me she was 'a rockstar' but couldn't even sing.
My brother is a jackpost. He said he was 'the smartest person in the world' but got a C on his test.