Thanks, but No Thanks
It’s a shame that servers have to work so hard for so little. They rely on the kindness of complete strangers to make a living wage, so any bit you give after service counts. Well, almost every bit. If you’re a nasty, spoiled customer who complains about everything, you’re going to get what’s coming to you.
Nobody hacked a loogie in the Karen’s meal, if that’s what you thought happened. After the Karen handed over a less-than-two-percent tip, the OP decided to respond by saying that they should keep the money since they’re clearly struggling. Nothing makes a Karen angrier than insinuating they’re not financially well-off.