We've all heard that Parisians are rude. I don't believe there are any more rude people there than anywhere else. I do believe that the French take their culture seriously - and why shouldn't they? It's their home and we should respect that.
With all the reading I've done over the last year the one thing that I've read over and over again is this: when you enter any place of business, whether it be a restaurant, a grocery store, or the local boulangerie (bakery) make the effort to say "Bonjour Madame/Monsieur" and the same can be said for leaving - say "Au revoir". Think of the person as hosting you in their establishment. It's almost like going to someone's home. No matter how bad your french, make the effort and it will appreciated.
The following article talks about this and other things: Visiting Paris? Follow These Rules.