It might be useful to learn how to block unwanted users on YouTube, especially when you are being harassed through pesky messages and comments on your channel. This simple guide will walk through the different steps to block an undesired user on YouTube.
How To Block Users on YouTube
Go to YouTube and click on the user's name to access his channel homepage.
Navigate to the About tab, click on the Flag menu, and select Block User from the list:
YouTube will display a small warning message asking you to confirm your decision. Click on Submit to proceed:
That's it; the blocked user will no longer be able to contact you through private message or comment on your channel.