a ham
A ham is a person who acts like a total idiot just to be the main show. They're usually kids who think they're the king of the world when they're around strangers.
My cousin tried to dance on a table at a wedding and fell over. Classic ham move.
My little brother told a joke so bad it made my grandma cry. He's a ham.
At school lunch, my friend tried to do a magic trick with a sandwich and it exploded. Ham alert.