If you don't live in the five boroughs you probably won't know exactly what a "store sidekick guy" is; allow me to explain.
A sidekick guy is a neighbourhood guy, whos normally a little bit slow and down on his luck. He's got nothing to do but sit around a store all day and just make conversation with customers.
Rest assured 98% of his stories are utter bullshit or simply anecdotes he's stolen from years of eavesdropping on other peoples tales.
Most old school deli's have a sidekick guy. He's not on the payroll, he has no real purpose, he just sits on a stack of Posts, eats his buttered roll and drinks coffee all day. And talks about The Mets. Always The Mets.
Since the average day for a sidekick guy is spent listening to other peoples conversations, the sidekick guy is always privy to a bevy of useless, but interesting, information. Sort of like that nosey tenant in your apartment buidling or that old lady on your block who's always in everyones business. They're all cut from the same swatch.
Sometimes sidekick guy comes with a historical Brooklyn fact, but usually it has to do with current events, which he'll always take a suspicious stance on, and/or neighbourhood rumours.
I remember going to the hardware store once to get some wood glue and some graphite (Mittageisen for all you Siouxsie fans). So sidekick guy at the hardware store told us that a lady around the corner had a fire in her house and she had a pet monkey. And ofcourse the pet monkey had escaped during the fire and was now on the loose in the neighbourhood.
This is the type of priceless information you can expect from a high quality sidekick guy.