Attacking with an immature, frontal assault won't work well; it will prove that the attackers are immature and will only make you look bad. You need to be reasonable about this, despite the fact that someone stole your hard work.
First, try contacting them via PM on YouTube, if they don't respond within 48 hours or respond negatively, then reach YouTube's customer service about it. They'll be your best bet to remove the vid.
IN all seriousness, the truly best way to fix this issue is to simply ignore the oter person's video. Getting people to go on his video to comment, you;re giving him views. Just link people to your video and all will be well; outta sight, outta mind.