PureDangles
YTtalk Mad
I dont know if i would delete bulling comments, but i would probably try to step in and isolate the conversation. Youtube has a great tool where you can type in words or phrases you want flagged in comments so you can review them before they go public on your video. I use this tools for spammers so things that get flagged are "my channel" "my video" "Check out" "My" it does a great job of not even letting those comments get put on your videos.