There's a YouTuber I used to watch, CinnamonToastKen. It was pretty good, family friendly fun of him and his buddy just making fun of reality shows and stuff. One of those shows was this TLC thing called "G*psy Brides", which is about Romani people acting like rednecks and that being funny for some reason. It was at this point, that I began to realize that neither Ken nor any of the commenters realized that the G word is a genuine slur. That wasn't the dealbreaker though, that came later when he said in an aside during a video that he was told by someone that it was, indeed, an ethnic slur.
So Ken's response to this was bewilderment and his immediate assumption was that this wasn't a real thing and just another instance of "people being offended for others." So he decided to ask his community if it was really a slur and to leave an explanation in the comments. Because, y'know, that's somehow easier than just googling it. He ended up hearting a comment that gave a childish oversimplification of the issue that ultimately said "Some people feel that way but most don't care"
To this day I feel disgusted that instead of taking the L about his accidental racism, he just assumed it was a made up issue and then chose the one comment that protrayed it as some trivial thing. I guess I should've known he wasn't on the up and up when half his videos were collabs with Pewdiepie.
I just used to watch Barnaby Dixon, a puppeteer on YouTube. His channel was wholesome and decently big, he was even a guest on Adam Savage's Tested channel a few years ago. But then he started doing some interviews, and one time he interviewed a transphobe about children transitioning. When people were pointing out how awful this choice was, and how wrong and harmful everything the guest had said was, he just replied to the transphobes and ignored all criticism. So these days I stay away from pretty much all channels unless they are explicitly trans allies.