Board Thread:Support Requests - Community Management/@comment-5706853-20140621195548/@comment-1038387-20140621200842

Protip: you don't need proof. Admins can ban people at their own discretion. If you suspect a user of sockpuppeting, you can give him a ban. A short one, with a warning that the next will be longer if he continues.

And for attacking another user, you can also ban him. Explain that the behavior is unacceptable.

Edit: wait, you never said you were an admin. If you're not, take it to local admins.