if you're a uBlock Origin user (or use an adblocker with a similar cosmetics modifier), you can add these commands in the uBlock dashboard (under My Filters) to get rid of it!
youtube.com##+js(set, yt.config_.openPopupConfig.supportedPopups.adBlockMessageViewModel, false)
youtube.com##+js(set, Object.prototype.adBlocksFound, 0)
youtube.com##+js(set, ytplayer.config.args.raw_player_response.adPlacements, [])
youtube.com##+js(set, Object.prototype.hasAllowedInstreamAd, true)
This is coming from /r/pcmasterrace, so I don't know how accurate it is. Worth a shot if you want to keep using that site.
If I ever am forced to watch ads on that site then I'll stop using it so fast.
I originally got an adblocker when they first introduced video ads on YouTube. Banner ads and like block ads next to videos were bad, but it was easy enough to ignore them.
I constantly forget that ads are even a thing. I just refuse to deal with it.
I instantly go
when an ad is sprung upon me, it feels like the privacy of my mind palace is being violated