Man walks into a bar(long)

...he's a stuffy, fussy looking guy. Asks for a 20 year old single malt Scotch. This request gets the attention of 3 knuckleheads at the other end of the bar. The bartender says (to himself), "Who does this guy think he is?", and serves him a glass of Scotch from the well. The customer takes a sip, and gives it back to the bartender, stating "This is not even an aged Scotch. I want a 20 year old single malt Scotch. Impressed, the bartender takes down a bottle of 8 year old Scotch, pours a glass, and gives it to the customer. He takes a sip, and returns the glass, stating "This is an 8 year old blended Scotch; I asked for a 20 year old single malt Scotch". So, the bartender takes down a 15 year single malt Scotch, pours it out, and gives it to the customer. He takes a sip, correctly identifying the age, and returns it to the bartender, asking again for a 20 year old single malt Scotch. The bartender pours again, concealing the label from the customer, and, after taking a sip, the customer smiles and declares his drink a proper 20 year old single malt Scotch. And, in amazement, the bartender takes his hand from the bottle, and verifies that it is indeed what the customer ordered. One of the three drunks from the other end of the bar walks down with a glass, and asks the Scotch specialist to taste test it. He raises the glass to his lips, takes a sip and sprays it all over the bar, exclaiming "This is piss!!!" "Yes "says the drunk, "but how old am I?"