The smell that is emitted from one's crotch area when heat is applied. Synonym of crotch vapor. Not to be confused with a <fart>. Ass Vapor is more like <funk> that is reactivated by heat, usually after being dormant in the closet overnight.
Steve had to disconnect the seat heaters in his car because Mr. Miller often wore the same pants, and it caused Ass Vapor to be released.
I couldn't wear my black pants for a third day, when I touched up the crotch with the iron, they wreaked of Ass Vapor.