Brewer's: Cap and Bells
Wearing the cap and bells. Said of a person who is the butt of the company, or one who excites laughter at his own expense. The reference is to licensed jesters formerly attached to noblemen's establishments. Their headgear was a cap with bells.
“One is bound to speak the truth ... whether he mounts the cap and bells or a shovel hat [like a bishop].” —Thackeray.
“Here I was got into the scenes of my cap-and-feather days.” —Cobbett.