If a bunch of you want to be all politically correct ok, but people and places don't get reputations for no reason... Yes the people in NYC can be delightful, but when the song says "live in California once but leave before it makes you soft, live in New york once, but leave before it makes you hard", I think people from Brooklyn and the fast pace of NYC have established a reputation for people that may not put up with cough not withstanding the average person one to one maybe very nice...
The rudest people I have found are in Russia, I think Russians can generally be rude to each other and rude to everyone else, yes i'm sure you can get some amazing bonhomie out in the regions and they will give you the shirt off their back, but i think they do have a reputation of being a touch brusque and unsophisticated perhaps not surprisingly from being caught in a time warp for most of the 20th century while other cultures were mingling... I have been in quite a few cities in Europe and you see a bus rock up and vomit out these bunch, the women are all over make-upped and tarted up and the guys all think they are he-men and god's gift more often than not... I think more than a few service oriented jobs I have heard rate the Russian's pretty low as well...
I have been in Paris and have met rude Frenchies, up the top of the Eiffel Tower with the ex and when the doors opened in the lift they all surged forward diregarding any semblance of a line and this guy hurt her arm, anyway on the way down she let him know that he had hurt her arm, I was standing a bit away because of the surge in and when she exited the lift he (with his family in tow) started making these simulated spitting sounds toward her back and carrying on, till i tapped him on the shoulder and he was off like a rat up a drain pipe, if he had been actually spitting (something that the Frenchies can be known for) it might have been a different story.... I do know a few words of french and usually start conversations with a Parlez vous Anglaise etc and a a few words of welcome so don't usually have a problem and get by with them although did call out a guy on my most recent visit there and its best no to go into the schemozzle at the boarding area of CDG...
So yes, traveling can dispel some stereotypes and misconceptions, but it doesn't mean none are true or weren't once but may be changing over time... If the French acknowledge that they are either somewhat rude or, almost as bad, have a bad reputation of being rude and need a bit of work i see no need to step in and try to tell them they are all amazing...
Sydney again is a big city and i think in many big/mega cities they are a slightly different type to the smaller places or regional places in many countries.... Perhaps not surprisingly with such a crush of people and other factors...
The Germans, well its no surprised people have run into one or two average ones, again the reputation they have built up is probably not without cause...