The site Travel Etiquette attempts to unravel the mysteries of proper etiquette and social customs around the globe by providing advice broken down by country. Here's a snippet on how to mind your Ps and Qs in Argentina:
"…punctuality is not rigorously adhered to in Argentina. It is not considered rude to be 30 to 45 minutes late for a dinner invitation…."
Based on my experience, I'd have to agree with this statement. Argentines tend to hold a more relaxed view of time and are rarely punctual when it comes to social events. If you're a stickler for timeliness, try to loosen up a bit or else you will go insane here.
On a related note, friends and family don't generally call in advance to arrange a visit. Be prepared for visitors who drop by when you least expect them, as well as last minute invitations to asados and other get-togethers. Plans are made very spontaneously here, so just go with the flow. [Tina from Tina Tangos talked a bit about this recently on her blog.]
Here's another cultural difference that the Travel Etiquette article highlights:
"…don't be alarmed or surprised to hear what you might consider to be name-calling or swearing amongst friends. In this instance, political correctness certainly does not rule supreme, and Argentines might readily use phrases such as 'fat'…when talking to friends."
I can't tell you how many people here have descriptive nicknames like "El Gordo" (Fatty), "La Rubia" (Blondie) or "El Negro" (in this context, usually used to refer to someone dark-complected or olive-skinned but not necessarily black). I'm fairly certain that most women (and probably a few men) in the U.S. would be horrified if their friends christened them with a nickname like "Fatty," but it really and truly is not considered offensive here.
The Argentines call a spade a spade, and no one gets worked up about it. That's not to say that these words are never construed as an insult—it's all a matter of context and tone of voice—but among friends they're regularly used as terms of endearment.
Read the full text on etiquette in Argentina, and add your two centavos' worth in the comments.