I was just thinking this. He's the type of bully that my mother used to say "throws stones and hides his hands". He desperately wants to be liked, and wants to sit at the cool kids table, but is in essence, a very unlikable person, who doesn't want to be seen as a bully.

On occasion, he will do the bullying himself, (when there is no chance he will be held accountable for doing so), but I also observed that he is content to let others do the bullying in his stead, and finds that just as entertaining, because he will gleefully retweet the bullying of others, encouraging and abetting their behavior, and then go, "I didn't say/do it. He did it!"