Labunchkin
A person who acts like they're king of the hill, but they're just a fraud who can't back up their big talk with any real talent.
My friend is a labunchkin. He said he can sing like a rock star. I heard him scream at a cat.
My teacher is a labunchkin. She said she can do 100 push-ups in a row. She did 3 before crying.
My brother is a labunchkin. He said he beat up a gang of 10 guys. They were all 6 years old.