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!