I guess it depends on what like happens on your slack. I know that my company's version of it is used almost exclusively for business. People have tried to make jokes on there before, but it's not a great platform for that, so yeah we usually don't. I don't think we are humorless people; just knowing where to stick it. If your place had a different attitude I can see the Nazis comment being fine. It's certainly not worth making a big deal about. But to only care because the employee is a Jew is like: facepalm stupid.