This isn't really a situation of overly aggressive requests, but it's uncomfortable all the same. Here in Chile when you pay by CC there's no line for the tip - it has to be added in at the moment the card is processed, so every server, everywhere, will ask you directly if the tip should be included. Usually it's not a problem, but when you don't want to leave a tip, or less than 10%, it can be awkward. Having the option to fill in a line (or not) on the slip or leave some change (or not) once the server walks away is one thing, but having to say "no" to him/her directly takes some getting used to. Luckily (?) service here is uniformly crappy, so I got used to it quickly.