Last night, I ordered a small pizza for around $13 roughly, with nothing else to go with it. As I signed the tab, I noticed the grand total was over $18, which included the 'gratuity' and 'service charge' both, plus another blank line for additional tip. I left that blank and signed it, and as I handed it back to the waiter, I got the distinct impression that he was not happy.

What do you usually do in cases like this? I figure a roughly 35% add-on is more than enough. I know the service person doesn't get all of that, but can't one assume they get the auto-gratuity at least?

This is in a South American Radisson, if that makes any difference.