How funny is this joke?...really?

this guy goes into a bar and orders 30 year old scotch...well the bartender only has a small amount left so he figures he can trick the guy and just give him the younger less expensive scotch...the guy takes a sip and says "no dammit i asked for 30 year old scotch this is 15 year old"...the bartender again tries a different type."no!" the guy says. "this is 20 year old scotch i just want 30 year old please!" so the bartender gives up and gives him whats left of the 30 year old scotch. "im impressed you can tell the age of scotch" the bartender says. at that very moment an old man at the end of the bar pes the guy a gl of something and says "here try this" the guy takes a sip and spits it out everywhere. "gross! what the hell is this!?" he yells. the old guy responds "its my piss buddy! tell how old i am!"