I think he's equating the different flavors of self professed socialists who get into a tizzy any time someone makes a joke online with Nazism. And also, I think it is deliberately hyperbolic so that only people with a sense of humor will refrain from getting in said predictable tizzy about it.
I think it's funny because it's only to the people the term applies that it isn't funny to draw the comparison. It's like a joke about the people who don't get the joke, it's very meta and it's an inside joke that most people get.
