This happened to me a couple of months ago. I was at a rather fancy wedding in Toluca, Mexico. At the end the waiter who had been serving our table came up to me and rather aggressively demanded a tip. Not wanting to cause problems and not sure of the customs in that city (I'd been to weddings in other parts of Mexico where this didn't happen) I gave the guy 100 pesos. It was a wierd experience since typically this is covered in the total cost of the wedding.