I also used to bartend, and the customer is always right... (unless you're shutting them off from another drink and they're arguing...)
Besides, when you consider the actual cost to produce the drink, you must admit there's quite a profit that can be made on drinks. It makes more sense to replace that $7 froo-froo drink that really cost about $2 to make, than it does to tick-off a customer....
Like JRC said.... So, what really happened? Methinks there was a problem about a drink and it wasn't replaced or taken off the bill... am I close?