a legend in (one's) own mind

A person who affects or believes that they are of greater importance or notoriety than is actually the case. A humorous, ironic twist on the phrase "a legend in one's own lifetime." The assistant manager acts as if she's the only one keeping the company together. She's a regular legend in her own mind. Dave had one hit song, and now he's a legend in his own mind? Can't say I'm surprised. A: "Man, that guy sure is a legend in his own mind." B: "Yeah, I don't think anyone loves him as much as he loves himself."