Since someone already mentioned Youtube Poop, I'll add AMV Hell.
Youtube actually had a message system on the home page a while back I believe, but it was implemented in such a shitty way that nobody used it, so they killed it off. Now I think you can only message channels in a way that's buried under like 5 menus.How it felt more like a community. I actually made friends there in my first 5 years there. You could message someone you were friends with. I'm not sure if message are even a thing anymore. I don't know how to get to them if they do. Sadly Youtube deleted all old message a few years ago. I usually got spam anyway. Which reminds me on how I sort of miss chain messages. You know those one that tell a scary story of someone who died and if you don't forward it they will come and kill you.
People hated that when it was around because of all the Reply Girls who spammed vapid babbling under every popular video with their tits hanging out. If only we'd realized that was the lesser evil to the algorithm bullshit that exists now...Remember Response videos?
videos related to video you're watching?
I miss that.