I don't give a shit about Nazis.
Yeah, Nazis were horrible. Do you not have a problem with Nazis?
No, this is just a joke. I'm just being stupid.
The holocaust was a traumatizing event for many people and it can be hurtful to be reminded of it even by mentioning parts of it. You should go to a holocaust museum to understand what happened there and why it can be hurtful.
It's not even that serious.
I believe it is, because even today Nazis exist and they are causing a lot of trouble. Don't you think trying to mention or joke about them would give them more exposure and desensitization? Maybe it would be more wise to just never give them the attention.