By the way, people from Bueños Aires are called "porteños" (like, people from the port). And there is little a porteño likes more than a firm "no." This is often delivered with a slightly pursed lip and briskly wagged finger. For example, you go into a store and ask if they sell a certain thing: "NO."
I actually find this helpful, since the alternative is often a burst of rapid-fire information most of which I don't catch. But I think the best example of the porteño "no" is in the local "you're welcome." You occasionally hear "de nada" when you say "gracias" here, but it's much more likely that you'll hear "No, por favor" ("no, please.") And not inflected like "Oh gosh, I was delighted to do it!" Inflected a bit like "Oh for heaven's sake don't be a ninny." So you think you really made a mistake in saying "gracias" in that situation, until you figure out that's the way this exchange is supposed to happen. This is not a city of cuddly interactions. I love it.
A second social thing it was good to figure out: the basic jocular greeting from a taxi driver or empanada guy is "¿Qué tal?" Which even though it means (I think) "What's goin' on?" you are allowed to respond with a generic "Fine, and you?" Big relief.