The tag.user system was in place for a while but was cancelled because of lack of interest. You still see it on older posts, but nobody ever really gave a shit about it, and it this got canned in favor of more tagging options. Cases like this would support its reinstatement, but I think that shop has sailed.
What do you mean it was cancelled? Because I use #music.Existentialist so others can filter my poor music taste. It looks like it works.
I don't really mean something similar to that, although it would work. I essentially mean ability to "and" filters. Lets say your vegan and I'm vegetarian. I like your posts normally, but we keep butting heads in #vegetarian because you and I disagree over the ethics of eggs. Right now I would have to filter (b_b) or filter (#vegetarian). Or try to guess which sites you'll post from most and ban them (eggsaremurder.com). These options kinda suck. If I could filter only when both conditions are met (b_b+vegetarian), then I could enjoy conversations with you without us getting into ideological battles. You could post your daiya recipes and I could post mac and cheese recipes without either of us needed to butt heads.
If you've got a user who you always butt heads with over a certain topic, you could try not always rehashing the same topic because by the third or fourth time you should know where it's gonna end. If you keep picking a fight with someone, you might kind of be a douche. Like, let's say you and I disagree about eggs. We hash it out on 3 posts you put up. By the time I see a 4th post about a similar topic from you, I shouldn't need to reiterate everything I've already said or make the same arguments I've always made because we've been through it before. If I do, then I'm more concerned with blanketing you with my pedantic viewpoint than having a discussion. I mean, go ahead, give a post a chance and give posters chances too. But you don't have to click every link in your feed. You don't have to pick a fight every time you see a comment you disagree with. There's a lot to be said for saying, "Nope, not worth it" and moving on. I think there's more value to strengthening your ability to do that, than removing any potential arguments from your view.