Hi there, you can try deleting comments and blocking the user. You can also manage comments by requiring pre-approval before they get posted. You can also report harassing users and content via YouTube’s reporting tool.
@TeamYouTube Hi, so you may or may not know, there have been a bunch of spam comments throughout all of YouTube's videos saying "Oh yeah yeah" and it's affecting the feedback YouTubers are getting from their audience/viewers. Can you please do something about this. Thanks. 
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Thanks. Twitter will use this to make your timeline better. UndoUndo
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