I don't see that many threads complaining about trolls, if at all. Whoever they are probably just need to grow a thicker skin.
Anyway, on topic:
I don't think I know any forum that has an Ignore function. Not sure why one would be necessary either since you can just simply ignore a user without external help. You could Block a harassing user I suppose, but that's why we have the Report function, and providing picture evidence helps them get b&.
If anything big red text saying "You have ignored this user" whenever they post would be more annoying than seeing regular posts. And potentially confusing when someone else quotes them.
Coconutt wrote...
Edit: for example doesn't youtube have in the comments the function to hide posts that a lot of people down vote, could that be possible? And if you wanna see the comment you can do so by clicking the "show this comment" or w/e.
With YouTube though, it's necessary. YouTubers are, most of the time, idiots. There's idiots everywhere, but YouTube has its own brand of idiocy.
Here I don't think it would work, partly because that kind of setup isn't really suited for a forum, but also because it could potentially be ripe for abuse - people making alts to purposely downvote entire threads with the intention of having every post hidden. That's what happened on YouTube when Google+ was first made mandatory, if I recall. Completely legitimate and inoffensive comments being automatically removed simply because it was that easy. I may just be jumping to the worst-case scenario though.