How did "humorless *****" become synonymous with "feminist"?

I've seen this a lot even when it's an anti-feminist strolling into safe spaces where feminists are *surprise surprise* making jokes and being merry. I'm a feminist and there's tons of things I find funny; especially when approached from a new angle. In fact the very minute I self-identify as a feminist, I am suddenly stripped of my humor. I'm no longer to talk about what I find or didn't find funny else and why or why not because I'm now a humorless *****. It's weird and annoying.