I'm chilean, thus I'm american because I live in The Americas, and I consider it's offensive when a US citizen says he is american meaning he is from US.

That being said, I can understand that "american" in english is widely used to refer to a US citizen and I can live with that, but what really bothers me is when someone speaking spanish refers to a US citizen as "americano", because it's not just offensive but also wrong, the reason is that in spanish the correct demonym for a US citizen is "norteamericano" or "estadounidense", and not under any circumstance "americano", that's totally wrong in spanish.

Anyways, I have many friends from the US and I have no problem in drinking a beer with them as long as they don't say in spanish they are "americanos", lol.

I hope this could help to clarify something from a latin-american point of view.