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.
The "Enhancer for YouTube" extension blocks YouTube ads and has an option to allow ads on whitelisted channels so you can still support creators you like.
It does a lot more too, I definitely recommend it.