Noun, the phenomenon where the drinker (typically of whiskey) crosses the line between amiable drunkeness and becomes a miserable fucking cunt.
Or
The name given to the metaphorical chastity belt imposed by a normally sexually generous woman in response to outrageously drunken conduct.
Mark, "I got so cunted last night I crossed the whiskey barrier and became so fucking depressed I could have cut my own head off if I was not so uncoordinated."
Or
Barry, "I'll just have just the one tonight, I am feeling fucking horny and I don't want the missus to drop the whiskey barrier like last time."
The act of giving a female a whiskey enema and corking it with a buttplug to hold in the whiskey effectively aging it like a fine wine until she cannot hold it anymore. She then squats overs your face and pulls out the cork releasing the whiskey like popping the cork on champagne!
Damn, Trevor celebrated being a new father by popping the top on the ol’ West Virginia Whiskey Barrel!