Navigate to your channel's dashboard and choose "Settings" from the left-hand sidebar. Click "Community" and then copy-paste the URL of the channel you wish to ban into the "Hidden users" box. When a person is blocked, they are unable to leave comments on any of your videos. If they try, the remark will not appear. Blocking someone also prevents them from liking or commenting on your videos. Users can be unblocked by navigating to their profile page and clicking the "Unblock user" button.
On their profile, go to "About," then click the flag button. You'll notice an option to "Block User" in the drop-down menu. When you confirm your decision to block this person, they will no longer be able to send you direct messages or leave comments on your videos or channel. They will also not be able to delete their Google+ account.
Remove a commenter's impediment
Unblocking or Unbanning Someone on Your Youtube Channel
Go to the Community tab under channel settings, where you'll see a section for "Blocked terms," where you may add words or phrases that you don't want to appear in your comments area. When someone includes one of these words or phrases in their comment, you won't see it when you read through the comments.
Log in to your YouTube account. Navigate to COMMUNITY > Community comments in the left-flag menu. Click the drop-down arrow next to the flag icon on a remark written by the user you wish to conceal. "Hide this user's comments on this channel" should be selected. Click Save Changes at the bottom of the page.
The comment will be deleted if it violates YouTube's Community Guidelines. Remove the user's identity. You may prohibit a user from commenting directly from their bad comment or in your channel settings' "Community" area. When you ban a user, they are not notified. They will be unable to comment or post videos through your channel.