I always prepay my gratuities and have no issue with it. I, however, do not care for how the drink receipts are printed out. The receipts on the Spirit for drinks call the built in tip of 18 percent a "service charge" and then list at the bottom "gratuity" (optional). I find this to be rather misleading and giving the appearance that you have not provided a tip. Most everyone out here knows this, but there are lots of blue cards that may not have a clue and then feel like they need to add a tip. On some ships I have seen it properly listed as "additional gratuity" which is a much fairer representation of what is actually going on.