I hear you, this is so hard. Even when the guys are good people, lots of people, especially men, just don't get feminism or are actively hostile towards it, and I find the rest of the group will usually go along with that.
My solution is to always be ready to fight my corner, but that is tough and draining, and doesn't work all the time because sometimes I'm tired and sick and there's too much sh**tiness. I can't and don't call out every sexist thing anyone says, because that would be waaaayy too much work. I do call out blatant things, or things from people who'd be receptive to me saying "Actually, that thing you just said was a bit yucky." Sometimes I've called things out and got backlash.
The most upsetting incident was when me, my partner and a good friend were watching Firefly, and my (sexist) housemate came in to watch it with us. Friend called something "Pimp!" at one point, meaning "Awesome!" and I was like "Uh, can you not use that word to mean awesome?" and he said "Sure, sure! Can I ask why?" I said "Well, I feel personally uncomfortable glorifying someone who sells women's bodies for sex*, it's a bit ... rape culture, isn't it?". Friend says "Oh, cool, I get it. Just wanted to know, that's fine!" Housemate goes "Rape culture? Pff. What does that even mean?". I shut the conversation down because I hate hate hate talking to this guy about stuff like this, because he's really contrary about it and sometimes openly very close to misogyny. Anyway, we kept watching, and the next episode was the one with the sex workers. I won't go into plot, but at one point a man in power abused a female sex worker in front of a group of men, and housemate goes, in really satisfied voice "Now THAT'S a rape culture!". Me:
(Later, I had a really affirming chat with Friend about the whole thing, he was totally on side and completely understood where I was coming from, it was great!)
*I know there's a big debate in feminist circles about sex work. Suffice to say most sex workers are women and most sex workers are trafficked, especially those who work under a "pimp" rather than independently or as a group of equals.
Soooo... It's hard. It's hard and it kind of keeps being hard. I think it's difficult to avoid, if you're a feminist woman in a male-dominated or male-centred culture like nerddom is. It does get better, because a lot of people, when confronted with a real example of whomever they're prejudiced against (a feminist, an atheist, a toddler, a Jewish person) find it difficult to keep saying sweeping statements when that now includes their friend Kender (I am only one of the aforementioned things, but I am some other things!). And it's great when you find an ally, and even better when you talk someone around from not identifying with what you're talking about (equal treatment, applied regardless of gender) to realising that's something they can get behind, like Friend in the previous story.
And my PM box is always open to talk about feminist things, Glass Mouse!