This guy is like Batman—except with preventing a toothbrush robbery by yelling for a cop to help, instead of, you know, with batarangs and martial arts and stuff.
When Kevin inadvertently steals a toothbrush from a drugstore—he panics after Old Man Marley enters, and then bolts—the clerk lady tells Jimmy, the stock boy, to chase him. As soon as Jimmy gets outside, he passes the buck to a cop, telling him that Kevin's a shoplifter. We don't see any more of Jimmy after that.
Jimmy's not very important, all in all. We bet Jimmy cries himself to sleep at night over what a minor character he is.