How can I deactivate YouTube on my laptop so that I can no longer open it? (In browser)
Not at all.
On Windows?
Go here:
% windir% \ system32 \ drivers \ etc
Open the hosts file with a text editor
Add the line
127.0.0.1 youtube.com
(and possibly all other varieties of it).
Save the file. Right click on it. Writers.
This intercepts all inquiries to the address entered and routes them to your own computer, which of course then only shrugs.