Years ago, in my early days of contributing to Python, I'd seen messages on mailing list that made me feel uncomfortable but I didn't feel brave enough to call it out. I brought it up privately to my mentor, and using his position in the team, he called it out and people apologized.
That's one of the things that stood out for me about mentorship. It's not just about teacher/student kind of thing. It's also moral support, using one's privilege for others who don't have it. (1/)