high on one's own supply

Etymology
From a scene in the film (1983), in which drug dealer Tony Montana  is mocked for excessively consuming cocaine from his own inventory.

Adjective

 * 1)  (of a drug dealer) Using the drugs which one sells, especially to excess.
 * 2)  Assigning too much credibility to exaggerated favorable descriptions of one's character, achievements, or prospects; intoxicated by one's own braggadocio; enamored with one's own overvalued public image.
 * 3) * 2013 June 10, Jonathan Owen, James Cameron: 'Don't get high on your own supply', Independent (UK) (retrieved 28 July 2021) :
 * The relentless pursuit of realising his imagination on the big screen has come at a personal cost. The director admits he used to play up to the "image of what a film-maker was supposed to be.  [D]on't get seduced by your own stuff. Don't get high on your own supply."
 * 1) * 2019 November 10,, Luckily, Trump Is an Unstable Non-Genius, New York Times (retrieved 28 July 2021) :
 * Trump seems to have gotten high on his own supply — he actually seems to believe the bizarre conspiracy theories his supporters drum up to excuse his actions.
 * 1) * 2020 November 4,, Election night TV was high anxiety, flat comedy, Washington Post (retrieved 28 July 2021) :
 * Tapper reminded viewers that there had been a lot of magical thinking lately on the part of Democrats and liberal pundits, who spent too much time entertaining pie-in-the-sky dreams imagining a landslide victory for Biden. "As they say, 'You can’t get high on your own supply,'" Tapper zinged.