If you refer to yourself as a doctor even though you never actually went to medical school, you are a soi-disant, or self-styled, doctor. Please don't try to operate on anyone.
This adjective is a stylish replacement for terms like "so-called," "self-styled," or "would-be." Your friend who appears loud and outgoing everywhere she goes, but describes herself as shy, is a soi-disant shy person. The word is also used in a legal context when the law disagrees with a person's self description, like the soi-disant ruler of a country who has illegally seized power. In French, soi means "oneself," and disant is "saying."