This has probably been said a million times before but: Defend the employees.
Really, you’re never going to see Karen from Stubenville again in your life, so side-eye her real good and say:
“It’s not thier fault they’re understaffed. Having worked retail before, they’d love to have another three or five people back there helping out. But since the whole ‘downsizing’ craze of the ninties, companies try to get as much out of thier employees as possible without regard for thier welfare, or the effect on service. You should really get on McD’s website and complain about the chronic understaffing and tell them you’re willing to pay more elsewhere for better service. They LISTEN to people like you.”
People love to complain, especially entitled people. The good news is that they’re easily redirected with mild praise and a shiny new target. Butter the elders and aim them at the bourgoise.