A person obsessed with their own (supposed) importance.(noun)
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Use "egomaniac" in a sentence
"I mean, there was other stuff on the line-up as well, other artists, each of them doing their album track and a few of their own songs, but most important of all (as far as this sad egomaniac is concerned, that is) was the fact that Aereogramme were FRICKIN PLAYING OUR FRICKIN TRACK LIVE!"
"For anyone to accuse you of being an egomaniac is ridiculous."
"That said, I also have to wonder what kind of an egomaniac is 78 years old and is being treated with chemotherapy for Hodgkin's, was recently treated for a brain tumor and has had double bypass surgery yet he has such a pathetic personal life that he wants to stay in DC instead of enjoying life with his family."