You can do and name yourself whatever you want as long as you do it in private. But remember: whatever "declaration" in public, even a post on SN is a public space. A declaration in a public space is a declaration of intent or self-determination and everybody will take notice. Any declaration in public have consequences (or at least you end it with "all rights reserved").

So calling yourself a "pleb" in public, is like screaming out loud that you are a slave.

Learn how to use public and private.