Wiktionary
n. 1 (lb en usually plural) The false belief that one is important or powerful, accompanying certain mental disorders. 2 (lb en usually plural) conceitedness or overconfidence.
Usage examples of "delusion of grandeur".
But a delusion of grandeur can be served only by the switching, undefinable chimera of a public monument—.
Every swine with a delusion of grandeur wants to set me up for something.
Some might have called it a delusion of grandeur, but IG-88-who had already been copied into three identical counterparts, his personality moved into separate droid bodies-saw no reason why he could not upload himself into the huge computer core of the new Death Star!
On the other hand, this could be an incredible delusion of grandeur.
If he controls even his own death, this is grandeur --a delusion of grandeur.