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.
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