I think jokes that make fun of Holocaust victims or make light of the Holocaust are extremely offensive, and I think it’s disgusting when people co-opt Holocaust terminology for non-Holocaust things (e.g. “feminazi”), but making fun of Hitler isn’t that bad in my eyes. The guy was a colossal asshole and tyrant and he deserves to be mocked in every possible way until the end of time.
It’s kind of like rape jokes: jokes making light of rape or making fun of rape victims are never okay, whereas jokes lampooning rape culture and making fun of rapists can be okay. (See “15 Rape Jokes That Work” for examples of what I’m talking about.)
The golden rule of non-oppressive comedy: punch up, not down. Make fun of abusers, tyrants, entitled assholes, etc. – not victims.