I just returned from a three week vacation in the US and have to say I experienced the rudest drivers so far in my life. Noone ever let us merge when we had to change lanes or enter an interstate, people even quickly closed gaps and honked their horn at us so that we could not get on.

Compared to this, drivers were very polite in (northern) Italy. We had no problems at all to changes lanes or enter the highway. People usually made space for us, as is should be in a civilized country.