My DF has worked in the tourist trade for years and years and years. He mentioned how "rude and hurried" many American tourists seem to be. This is what I explained to him:
A trip to Europe for the average American is a once in a life time trip. Costing thousands of dollars, and often lasting 2-3 weeks, people jet to Europe and get busy seeing all there is to see in as little time as possible.
When you take into account that they have flown across time zones, are jet-lagged, sleeping in varrious hotels every night, going to one or two (sometimes three) cities in a day, crossing into France then Germany then Spain and flying here there and the everywhere to soak up as much culture in one pop as they can, it is easy to understand why they may seem rude.
They are tired, with sore feet and ever-deflating wallets, are eating foods that are not the "norm" for them, if eating at all with the packed tour time table, and are hearing multiple languages and acents at every turn.
When you think about it that way, it's easy to understand why people come across as rude.
Of course, then there are those who are just rude. Regardless of where they are in the world and how much they have had to sleep...