buffoon
A person who acts very silly and foolish.
A buffoon is someone who acts ridiculous or foolish, often making a spectacle of themselves through silly behavior or clumsy mistakes. The word usually describes someone who doesn't realize how absurd they look, like a character in a story who keeps making the same mistake over and over while everyone else watches in disbelief.
You might see buffoons in old comedies or cartoons: the character who slips on banana peels, walks into walls, or says exactly the wrong thing at the wrong time. But the word also applies to foolish speech and behavior beyond physical clumsiness. A student who constantly interrupts class with random jokes that aren't funny, or a boss who makes terrible decisions while acting overly confident, might be a buffoon.
Calling someone a buffoon is fairly harsh. It suggests they're not just making an occasional mistake but behaving foolishly in a way that's hard to take seriously. When a leader acts like a buffoon, people lose respect and stop trusting their judgment.