A pro wrestling term. A wrestler gets cheap heat when he makes a direct appeal to the crowd: name dropping local sports teams or celebrities, or simply telling the crowd how awesome they are. Heels use the same tactic; they simply make fun of the local sports team or celebrities, insult the crowd, etc.
Also known as a cheap pop.
Wrestlers are not the only public figures to make use of cheap heat; comedians, bands, and politicians do the same thing. They just get called on it a lot less.
You think John Cena's a Mariners fan or is he just wearing that jersey to catch some cheap heat in Seattle?