The entire problem is that "saying 'bro' is poking fun of other men"! It is a joke, by men, about men, in regards to programming. To reiterate: a joke, regarding programming, written by men, that completely disregards women.

Of course, on its own, that is pretty irrelevant. There are jokes like that all the time on all sorts of topics. But in this situation, it is ALWAYS men joking with/about other men. Women are excluded from the jokes completely. And these sorts of "jokes" and other little implicit signals are all over everything remotely related to CS/tech. Which gets pretty discouraging, day after day.

"If it's not about women, it's sexist."

Ok.