Gerald: Guess who almost signed for unemployment today?
Billy: I give up.
Gerald: You... But Mr. Corben had second thoughts. He gets so sentimental around the holidays.
Billy: Imagine that.
Gerald: If it was up to me, I would have fired you in a second.
Billy: Well, a merry Christmas to you too.
Billy, although a kid, works in a bank to support his family (doing all kinds of blunders, hence the conversation). Everybody in his town sort of has small jobs, because the main factory just got closed down. Moreover, Mrs. Deagle, the landlady, is very mean, and won't condone people not being able to pay the rent. But Christmas is near, so everybody just puts on a brave face and tries to live through their problems...
Enter Gizmo. He's a cuddly, lovely koala-like sentient pet Billy's father found in New York's Chinatown. But the Chinese who sold it warned Billy's father against getting water onto the 'mogwai' (móguài actually means demon in Chinese) and against feeding it after midnight.
Of course, both events happen, and the nice, furry pet spawns an army of evil reptile-like monsters (the gremlins) who wreak havoc in the small town, drinking booze, smoking cigars, destroying property, burning out building, and killing Mrs. Deagle and looting the department store during a night of terror for the inhabitants.
Predictably enough, Billy and Gizmo manage to dispatch the gremlins. The morning after, news commentators who flock to the disaster-struck city describe it as having been the scene of riots.
For me, the film is an allegory of the Reagan era, and of how Americans should have reacted to it: by rioting, killing the landlords, looting the department stores. The gremlins are within us, as shown by the fact that they are created out of Gizmo's very body. They embody the anarchic tendencies that we all have but that we hide deep within ourselves.