We evolved to live and work in groups of 150, max. Past that our brains get overwhelmed and fall back to pattern matching, another evolutionary trait, and a powerful one in us humans.

We're so good at judging people that when someone's behavior throws us for a loop, it's a memorable event.

The only trick is making a conscious decision to stay the hell away from "all $people act like $X". Even if I think a customer walking up is likely to be a chud, I greet them openly and friendly. Works out great.