Facebook. It ruined the Internet.
Personally, reaction YouTube channels. Nobody gives a fuck what you look like when you’re watching a video and it’s all overacted nonsense.
Edit: People making good points, specialized/educational reaction channels are actually good with people in their industry talking about the intricacies of what they’re watching and giving you information you wouldn’t get by watching yourself. Corridor Crew does this very well with their channel where they have stuntmen/women, VFX artists and other specialists come on the show and talk about things you wouldn’t have known before.
HOWEVER, the channels that are literally just some random kid freaking the fuck out over a stupid video are absolute garbage. This includes most channels that react to tv shows or movies when they have zero experience in what they’re reacting to. I don’t want to watch someone shittily overact while watching an episode of Avatar. I WOULD watch one of the artists that animated an episode of Avatar explaining and reacting to episodes they worked on, like Corridor Crew does.
Top 10 slideshows with ads.
Ads or paywalls
Aside from the obvious choice of the stuff that’s already illegal:
All the conspiracy theories that are easily proven wrong that are just polluting the minds of the easily fooled.