If a man smiles all the time he's probably selling something that doesn't work.

Carlin’s line skewers the performative cheerfulness associated with salesmanship and public relations. The “man” who smiles constantly is framed as someone using friendliness as a tactic rather than an authentic expression—an outward gloss meant to disarm skepticism. By adding “selling something that doesn’t work,” Carlin links relentless positivity to deception: if the product (or idea) were genuinely sound, it wouldn’t require such aggressive emotional packaging. The joke also reflects Carlin’s broader comedic stance: distrust of institutions, advertising, and the social pressure to appear upbeat. It’s a compact critique of how persuasion often substitutes image for substance.