As an Australian who has travelled quite a bit and been part of many different expat communities, I find that Americans more than people from other countries do this one particular thing that annoys me.
When I am speaking, really about anything, just in general conversation, I hate being interrupted so that someone can impersonate my accent to me.
This is how it goes:
Me: "...so then I'd probably add just a little butter..."
American: "Buttah! Buttah...you say Buttah. Australian accents are so funny!"
Me: "Uh yeah, so as I was saying..."
So I have a different accent. I get that. But people not from Australia have a very different accent from me. I don't stop them midway through a conversation to repeat back to them what they said because, well, it's just rude.
Disclaimer: I love the U S of A. I spent some of the best years of my life there. I love most Americans that I have met (except for the jackasses).
So...this is not exactly an annoyance. But one thing I notice about some (many?) Americans that I don't see that much elsewhere is, they are eating or drinking something all the time. 呃······其实也不是很讨厌，但是我注意到有一些（很多？）美国人无时不刻都在吃东西，我在其他地方都没见过这样的。
Like, if they go to the movies they're munching on a huge bucket of popcorn or sipping on a bucket of soda through the entire movie. 比如说，如果他们去看电影的话，他们会津津有味地咀嚼一大桶爆米花或者狂喝一大桶苏打水。
If they're walking down the street they have a Starbucks latte or a Snapple bottle or something in one hand and a phone in the other. Or they are chewing gum.
They eat in the car all the time too.
The excuse I've heard for this is it's because Americans are so busy all the time that they have to eat on the run anywhere they can.
But still...aren't people in other countries busy too? It's a bit of a puzzle.
I get worried about Americans' response if I criticize something about the US.
Europeans and Asians are used to criticism from outsiders more due to multicultural geography and not take that criticism as hate.
Every now and then, when I criticize something about the US online, even when I'm very careful with my words to not offend anyone, I still receive some responses like, "First look at your own country!", "You're not from here, you have no right to say anything." "Foreigners hate America."
Americans have a lot of behaviors that while not being actually bad things, seem rude to foreigners.
Americans are loud.
It seems to be the norm here in the US, so you don't notice it a lot, but in other countries where people speak "normally", it sounds very rude/uneducated.
Especially in restaurants, where all the locals speak softly and politely to each other, and a group of people is like "OH MY GAWD, THIS FOOD IS SO GOOD, BWAHAHAHA, THAT'S THE SH*T DUDE!"
Everyone else in the restaurant is immediately thinking "Rude Americans".