To name a few:
Calling yourself Americans, after the entire dual continent. There are two continents and many other countries in the Americas, you know... [I know you know. And, what are you supposed to call yourselves, 'USAians'? 'Americans' makes more sense and is easier to roll off the tongue. But it's weird.]
Holding the door open for me. Smiling at me on the street. Those are sure signs of a swindler, but it's the norm in the USA. [I am not suggesting USA folks are swindlers, only that those actions are what swindlers in much of the world use. USA people are generally super nice and a genuine pleasure to be around.]
Turning right on red light. Red means stop. It's weird and confusing.
Edit: I added a third thing.
Edit2 in []
What shoes are those? Those are dope