Hover a thumbnail on youtube.com and click an icon at the right: "Not interested" and "Don't recommend channel"
< Feedback on YT: not interested in one click
It may happen if you clicked before the site loaded its scripts. I should probably display some kind of "Wait" message in this case....
In case of staying at top page of Youtube for a period of time, after reloading the page and pressing "Not Interested" on any videos, it sometimes shows a wrong message "My Ad Center". Nonetheless, this problem never happened in (youtube.com/watch?v=????????) page before.