jackbag
A person who acts like an idiot and doesn’t care about how they look. They do dumb things just for fun.
My cousin is a jackbag. He tried to dance on a table during lunch and got in trouble.
My friend is a jackbag. He tried to wear his pajamas to school and got laughed at.
My brother is a jackbag. He tried to throw a pencil at the teacher and missed.