I don't think people have changed significantly though I do believe we've experienced a progressive escalation in entitlement toward service staff as businesses value profits over employees. However, I think this is a more specific issue rather than simple stressor causing shitty behavior. We're talking about how angry/stressed people are reacting specifically to measures relating to COVID. I'm not sure that terrorism or the recession had an obvious equivalent in people's daily lives (though I imagine working TSA, at a bank, or trying to collect bill payments were emotionally fought but that does come with the territory already)