Everybody says this about Parisians, but I haven't found it to be true. I've visited Paris 3 times for a total of almost 3 weeks and met very few rude people. I've met a lot more assholes in Manhattan than in Paris. Of course, I follow the French rules of politeness. I always start with "Bonjour/Bonsoir" and always finish any visit with "Merci, bon journée/soirée, Au revoir." On the other hand, I've seen plenty of rude behavior by American tourists who just start speaking English to French people without any greeting or any attempt at French.