This web extension can block YouTube videos from view based on keywords or channel name. It features a very basic password protection and the block message is user-customizable.
Originally this was developed for a person who is easily scared and needed to be protected from certain youtube searches. Because there was no easy way to do this I developed this application. It is made for this person but published as an extension to possibly help other people who may have the same needs!
Get it in the Chrome Webstore
Or for Firefox
Find the source on Github