It's because they're weak, powerless little people. They realize that they can be absolute bastards to retail workers because retail workers can't do anything about it and have to take it or they'll get fired. So they get their little power trip feeling by abusing retail staff. Then usually complain to their corporate office and end up getting free stuff out of it. I worked in retail management long enough to see that pattern repeat regularly. Get told by someone at head office I needed to talk to some teenager about their attitude, and I'd see the email or transcript of the call from Karen, and knowing often as an eye witness that it was entirely made up, they would take the Karen's side, offer gift cards and apologies and the trend would continue.