On Tildes I don't have any filtered tags yet but I did unsubscribe from ~anime, ~books, ~food, ~games, ~movies, ~sports, and ~tv. Wow I just made that list and realized I cut out most of the fun groups... I'm not sure what that says about me haha. I unsubscribed from all of those because I either don't enjoy those things or if I do, I know what I like and don't have any inclination to discuss them.
Reddit is where I have the most things filtered out. Mostly entire subs from r/all but I have some users blocked too. Like poem_for_your_sprog. Don't get me wrong I like poems in the right context but it throws me off too much when I'm reading an askreddit thread and suddenly find myself reading a poem. A dumb pet peeve.
Facebook it's just random people blocked from showing on the newsfeed.
I have said "not interested" to videos on youtube more times than I would ever care to count. I'm not sure why but they have a really hard time giving me content I want to see. There's usually like 3 videos in the feed I'm down with and the rest is just garbage. They're good about not showing me things I said I'm not interested in but they can't seem to pinpoint what I actually want.