I've travelled quite a bit and these are the complaints I've heard: that Americans don't know about and aren't interested in other cultures; they imply that American ways are superior; that Americans talk really loud--mostly about money, which is considered rude outside US borders, but Americans don't know that; that Americans are obsessed with guns; that Americans are so frightened of each other that they need weapons nearby; that their eating habits run to large amounts of organized grease; that they treat wait staff like bad servants. I have been in several cafes where all wait staff refused to serve Americans and that seemed fine to their boss. This is the American stereotype internationally--which is quite unfair to all the wonderful Americans who aren't like this.
I believe this depends on the foreigners' culture. As it is, most foreigners usually report that the first thing they notice is that Americans and their culture seem fake and superficial. They say Americans aren't interested in cultivating anything else apart from money. Then again, this is a matter of personal opinion, so it is bound to vary depending on who you ask.