Tobacco Smoke Enema (1750's-1810s)
The tobacco enema was used to infuse tobacco smoke into a patients rectum for various medical purposes, primarily the resuscitation of drowning victims. A rectal tube inserted into the anus was connected to a fumigator and bellows that forced the smoke towards the rectum. The warmth of the smoke was thought to promote respiration, but doubts about the credibility of tobacco enemas led to the popular phrase “Blow smoke up one’s ass.”
I don't trust him, he's just trying to "blow smoke up one's ass".
Oh don't believe him, he's just blowing smoke up your ass!