A nasty ass after taste. Usually referring to cheap liquor that only goes down with a powerful chaser.
Steve: Hey Rochelle, this Samuel Grant Bourbon style whiskey has a NASTY assfertaste! With what shall we chase it down?
Rochelle: Honestly Steve, anything this gross ought to be chased with bleach or something of similar acosticity... But I suppose this liter of coca cola will have to do. It's all we have within a five foot vicinity, after all.