I'm originally from Argentina. Not everyone might know this, but the stereotype of Argentinians is that we are loud mouthed, vain, full of ourselves, and that we think we are smarter and above everyone else. That's without even mentioning our speaking pattern, which means we pronounce everything with a hard "SH" sound (like in "cashier").
I am probably as far from that stereotype as you can get, or at least I try to be. I try to be respectful, I try to be humble, and I even try to modulate my speaking, so people don't realize I'm from Argentina. I've got plenty of experience of this, when I was living in Miami, and half the population was from Central and South America. The moment they noticed you were from Argentina, the floodgates opened for all the jokes you can possibly imagine, to laugh at all the stereotypes of Argentinians, whether I had earned them or not (more often the case).
And you know what's the crazy thing? Even I will admit that the stereotypes are true. The majority of Argentinians I've met since I've left the country have fit comfortably into the stereotype. Not all of them, mind you, but enough for me to see why it was formed in the first place. Some of them are even part of my family, but they are not as bad as others.
There was one memorable occasion, where my wife and me went to a family dinner (it was one of my cousin's birthday, I believe). She's already used to my family, and pretty used to my extended family. One of the invited people, however, was a friend of theirs, not a family member. This man was exactly how most people imagine the Argentinian stereotype to speak and act like. Loud, thinking he was the smartest person in the room, and spoke with an incredibly heavy accent.
After the dinner was done, and we were heading home, my wife asked me what his deal was, why he was acting that way. You see, it was so incredibly over the top, that she thought he was putting on act, being incredibly
obnoxious Argentinian on purpose. No way could someone be like that. And yet, he was.