A vegetarian is a person who won't eat anything that can have children.

Brenner’s line is a stand-up style definition-by-misdirection: it reframes vegetarianism not as a dietary practice but as a moral squeamishness about potential life. The joke hinges on an exaggerated criterion—“can have children”—that sweeps in animals while implicitly excluding plants, and it plays on the cultural association between vegetarianism and ethical concern for living creatures. By reducing a complex set of motivations (health, religion, environment, animal welfare) to a single, absurdly broad principle, the quip satirizes how people often caricature dietary choices. It also pokes at the boundary problems in food ethics: where, exactly, does “life” begin to matter in what we eat?