Flea Protestor

A background agitator glimpsed for a few seconds, marching with a sign on behalf of fleas rather than any cause a person might expect. She shows up mid-crowd, shouting slogans with total sincerity, one more voice in a Futurama protest scene where the target of outrage is deliberately, gloriously small.

The joke is entirely in the premise: someone somewhere has decided fleas deserve a placard and a chant, and the show never explains further because it doesn't need to. Tress MacNeille, a utility player across the whole series, gives the line just enough conviction to sell the absurdity without winking at it.