This is most often said to me when someone uses an ableist, racist, or sexist term. So yeah. Unfortunately, the majority of my friends are not as knowledgeable and conscious of problematic things as I am (now).
The other time this is used is when I fail to grasp that someone was being sarcastic, especially online.
I’m good at detecting sarcasm, but yeah I’m often thought of as the one that doesn’t have a sense of humor when I hear things that are HONESTLY some kind of -ist… My sense of humor is pretty fucking terrible but sometimes I hear things and I’m like dsfdsfga NO PLZ