In line recently at a Winn-Dixie supermarket in Florida, John DiDonna worried that a nearby shopper was standing too close for Covid-era comfort. DiDonna asked him to take a step back. The shopper, he says, stepped even closer. DiDonna says he snapped. “Do you love me that much?” he barked. The other person argued back; DiDonna retorted with “a sprinkling of four-letter words,” he says. “Afterwards, I was mortified.” The theater producer in Seminole County, Fla., says he has a shorter fuse these days after 18 long months of the pandemic, grappling with decisions about masks during rehearsals, employee vaccinations,...