This is why I never believe TiFs who say they "never experienced sexism" and it wasn't a factor in their transition. They do experience it. We all do. But it's often so subtle and we're so conditioned to see these things as normal we've learned to ignore when our guts tell us we're being mistreated.

You're not being paranoid. I think the first step to fighting back is to recognize when it's happening, like the situation with your friend. In order to avoid falling into the kind of thinking where you're looking for something that isn't there, try to compare the way certain people react to men vs how they react to women. Some people are just assholes and will treat everyone like shit, but sometimes there's a difference between how they interact with men vs women and when you know what to look for it's easier to spot.