Comments which are extremely aggressive, insulting or otherwise extremely abusive should be reported to the DeviantArt Customer Service Center.
Please keep in mind that staff may not be able to assist you if you have not already blocked the deviant you are reporting.
When reporting deviants please be certain to be clear in your explanation and to include the link(s) to the comment(s) which you wish an administrator to review. In order to link directly to a comment you will need to right click on the timestamp, located next to the username in the comment box and click Copy Link Location (or Copy Shortcut - depending on your browser). Paste (right click and select Paste) these URLs into your customer service ticket.
Be certain to also identify the profile which you are reporting by name.