IIRC, there was a writer on the net with the moniker Mary Sue. She wrote something called "Slash Fiction", which takes popular characters from tv shows, books, movies and musical groups and puts them in erotic (usually male homoerotic) scenarios. Often women wrote/write male homoerotic scenarios -- maybe its the female equivalent of hetero men drooling over pictures of "lesbians". But anyhow Mary Sue effectively "wrote herself into the script" and had "herself" have a romantic heterosexual fling with some media personality in her story. This caused howls of derisive laughter and to this day, anyone that writes themselves into their own script for ego-stroking purposes (or to stroke something else) is called "Mary Sue". I imagine that this could apply to a DM with a "Pet NPC", even in a non-erotic context.
Hope that helps.