How would that work? Even if there was a way to block them, they could just go on youtube without logging in, or with a different account to watch your videos.

And I mean, that’s just a stalker you know about. If you have enough viewers, there are also going to be others you don’t know about, so doing the classic “don’t post too much information about yourself on the internet” would still be a good idea, even if there was a way to block that specific viewer.

If you absolutely need to upload everything you do, maybe do it with a time delay, so the stalker only ever knows where you were, not where you are.