A friendless Man or Woman who sits at their computer 24/7 trolling YouTube pages to send random abuse to people. These people will go to great lengths to find out personal information to use in arguements, that they wouldn't have the courage to have in real life.
A youtube bully dominates your instant message conversations by repeatedly linking you to youtube videos and expecting you to watch right away.
Some youtube bullies are actually reluctant to watch videos YOU link them to, also.
Friend: Hey, watch this comedy skit! <youtube link>
Friend: What did you think?
You: heh. funny.
Friend: Watch this one, too. <youtube link>
Five minutes pass.
You: lol. ok watch this: <youtube link>
Friend: Sorry, I'm busy.
You: youtube bully.