give (oneself) airs

To think or behave as though one is superior to others or better than one really is; to have or assume a pretentious or self-aggrandizing attitude. I think John is really a decent fellow at heart, but I really wish he wouldn't give himself such airs about his writing abilities. Stop giving yourself airs, Mary, you're not some world-class actor—you're just an amateur like the rest of us! Do we really have to go to another arty-farty lecture at the art museum? The people there are so annoying—they always give themselves airs.

give yourself airs

act pretentiously or snobbishly.

1948 Christopher Bush The Case of the Second Chance It was said she gave herself airs, and it was also hinted that she was no better—as they say—than she might be.

Air in the sense of ‘an affected manner’ has been current since the mid 17th century; from the early 18th century the plural form has been more usual in this derogatory sense.

ˌgive yourself/ˌput on ˈairs

behave in a way which shows that you feel you are important: The nice thing about her is that, in spite of being so rich, she doesn’t put on any airs.