I can't generalise every American and the most time i spent in the US was a few hours at LAX waiting for a flight to Vancouver but every single American i've ever met is at least 2 of these things; loud, arrogant, fat, overly self important.
To illustrate the fat point, i was at terminal 3 and had to got terminal 5 at LAX (or the other way around, idk) and had no idea which direction is was so i asked one of the workers who was like "Well its around that way but its a bit of a walk. Shuttle comes from there if you wait". I was like, nah i'll just walk. Guy looked at me like i had just said i'd fucked his sister.
I can't debate you about the fat thing. Every time I come back to the U.S. I am so disgusted. I remember being on a flight back to the U.S. from Paris, 12 hours to Houston. The only people I saw in Paris that were fat were Americans. After landing, the seatbelt light goes off and a woman about 3 rows ahead of me reaches up to the overhead compartment and all I see is arm fat hanging and jiggling. I was disgusted and knew I was back in America.
The American car culture has made us extremely lazy when it comes to walking. I regularly walk to the store that is about 1/3 mile away. People think I'm crazy for doing so, and its not even that far away.
Don't even think about telling Americans they should speak more than one language. You might as well say you're a devil worshipper and sacrifice puppies and kittens.
Anytime I run in to Americans in a foreign country, I am usually appalled. Demanding people in their own country speak English, being loud, and generally displeasing. When in France, I almost always refuse to speak English, even to tourists.