When you are watching YouTube on the right you get some video suggestions. Many of them are terrible and often have insulting thumbnails (retarded faces, clickbait and that kind of stuff).

Until recently you could click on the suggestion and select "don't recommend this channel" to block any video suggestion from that channel, but few weeks ago they removed it and I am again bombarded with crap.

Any way to block entire channels from appearing in suggestions on the right ?

Doubt it. Dumb clickbait thumbnails are pretty much a fact of life on the internet as a whole.

They absolutely push dumb stuff, just like how Steam pushed MMOs and online shooters at me constantly despite me never playing a single game from those genres on Steam, and blocking the tags. Internet gonna internet.

Hopefully someone tells you about a super secret option somewhere, but I'm pessimistic.

Well, apparently that's the youtube's goal.

I don't know if UBlock Origin can block them out but an easier solution would be to make the video itself bigger (either full-screen or most of the screen).

They also push certain political views. If you search news for certain countries or political leaders all you get is negativity. But media is also to blame, because they feed on negative news. Such control of information is highly dangerous.

I watch YT in theater mode (the button next to fullscreen in YT player) which pushes "up next" suggestions below the video.

I recommend these Firefox Add-ons:

Enhancer For YouTube

Ghostery

Privacy Badger

AdBlock Ultimate

It should make a big difference; they may be disabled under Tools/Add-ons Manager

So many people are complaining about YouTube suggestions. Yes, they often are quite silly. And yet YouTube introduced me to some really nice channels and music bands. I always browse the internet in private mode (adblock on) with geolocation turned off (like it have any difference), maybe it has something to do with that.

they stopped promoting nazis and eugenics when they changed the algorythm a while back.

I love those guys!

Google is the devil, plain and simple. Facebook and Twitter are arguably worse, but it's still way up there. Something I noticed is how certain content about touchy subjects is rendered near-unfindable, while vetted, "safe" opinion pieces from lamestream media outlets on the same subject are pushed to the forefront of search results.

A nice recent example would be that video of some ABC anchorwoman venting her spleen about being forbidden by her higher ups to report on Epstein's sex slavery ring and the political figures (Prince Andrew, Clinton) involved. The original Project Veritas video is buried, instead searching for it you'll get swamped with "safe" opinion pieces by CNN/FOX/NBC and the rest of the lot. Speaking of Project Veritas, they did have some kool videos about the inner workings of google/youtube.

Would you be so kind to explain the meaning of your post. I'm a bit sleepy and can't think straight at the moment, however I can't get to sleep either because I HAVE to know what you meant by that, I really do. Please help.

Literally the term "music band" reminded me of that t-shirt Steve Buscemi is wearing in that shot. It's a joke from 30 Rock in which he plays a private detective a few times. He (thinks he) is under cover in a school in that scene.
Sorry for not answering sooner, I was asleep and then at work. Hope you managed to get to sleep eventually!