Some things that may shock you about "rude Americans"
1) Line Etiquette
Cutting in line is a humongous no-no in the US.
If you want everybody in the line (including Grandma) to beat the crap out of you just try and cut-in a line.
People believe in fairness to whoever got there first...even to the point if you are in the middle you can ask the guy behind you to "Hold your spot" as you run off quickly to get that item you forgot.
2) Spitting
Don't spit in public. People will look at you like you are vermin (or an idiot teen). It's even illegal in many cities (but you'd have to really do something dumb to get fined)
3) Smoking
Depending upon the state you live in being a smoker can be rough. In many states you can't smoke anywhere inside public buildings. In fact you can't even smoke outside in the front of the building - you have to go out back..in a dark alley or something. You are treated like an alcoholic. Puffing away while walking down a city sidewalk isn't looked at as being "cool". It's more looked at as causing air pollution that people shouldn't have to breathe,
4) honking your car horn loudly at the person in front of you.
The person is going to turn around and hopefully not have a gun.
A gentle and extremely short beep is ok.
5) Using the elevator
Ladies first
When stepping on an elevator: Women board first.
When stepping off an elevator. If there are women near the front they get off first.
Oh and open and hold the door for her too