Has anybody ever spammed a tube site?
 

I am not a spammer, so i would not know how to do it. But it can't be that hard.
If you can spam websites, you probably already have the tools and knowledge you need to do this.

You would need a list of proxies and some automation software that uploads the videos to the tube site. Then hit the tube site hard with watermarked spam videos. The videos would need to have a minimum length or else they get filtered out. Randomly generate a list of generic titles and usernames for the upload.

If I knew how to get proxies (spammers have that knowledge) then I would do it.
Flood the tube with hundreds of watermarked videos daily. Hit them hard every day. If you don't want to do it yourself, pay some college kid to do it for you. Target only the ones that are proven to be illegitmate tubes and who steal your content.