Youtube is the site where SGF posts his videos. You can find his channel here. He sometimes shows up in videos on other channels, too.
The Chat and the Youtube watchers have a volatile relationship, and bizarrely high amounts of sexual tension. Youtube seems to be jealous of The Chat's close relationship with SGF, and The Chat is terrified of the ever-watchful eye of Youtube. Everyone else agrees that The Chat and Youtube just need to get it over with and classmate already.