Greasy Fork is available in English.
Hover a thumbnail on youtube.com and click an icon at the right: "Not interested" and "Don't recommend channel"
< Σχολιασμός για τον κώδικα YT: not interested in one click
Works for me and I have several other userscripts and extensions for youtube.
Not working anymore, no other script running and if it depends on nothing running besides this script, its not worth for me.