"You're already automatically paying gratuities when you buy a drink at the bar. Now I don't mind tipping ... but I was handing out an extra dollar for drinks without even knowing it!"

Indeed, most big-ship lines -- Carnival, Royal Caribbean, Norwegian and others -- automatically tack a 15 percent service charge on to bar bills. Unless the service was spectacular, there's no need to add another tip on top. Learn more about gratuities in our piece on cruise line tipping policies.