I would imagine a lot of unfriendliness would have to do with the "city face" that people walk around with. Regardless of whether you're from Buenos Aires, this is a huge city that presents danger to anybody. Walking around smiling all the time makes you more vulnerable. That said, if you actually speak to someone you shoud break through that "city face" armor and find a warm and caring person underneath. The people here are different than I'm used to, but can easily throw the adjectives "warm" "friendly" and "caring" out to describe them. I've had a MUCH easier time meeting people and making friends here than I did when I lived in Seattle.