Standing up to a bully doesn’t require fists. It requires a witness who refuses to laugh.

That kind of power depends entirely on an audience playing along. The laugh is the mechanism, and a single person who declines to supply it changes the arithmetic of the whole room, because the next person now has cover to decline as well. None of that requires a physical confrontation, which is worth knowing if you have been assuming the only options are fighting or nothing.

Be the one who does not laugh. Say something ordinary to the person on the receiving end, and tell an adult who has some authority afterwards.