My wife and I were in a line in the 1980’s to see the Sainte Chappelle in Paris (a stunningly beautiful chapel) and chatting with a couple of people in the line. Then, an American with a Texas accent walked up and said to no one in particular, “where do you get the f%@#ing tickets?!” Suddenly, none of us spoke English.
I loved Sainte Chappelle - the only place I ever gasped out-loud at. The rudest tourist ever was an Italian lady at the Louvre who used her infant-occupied stroller to ram and elbow her way to the front of the mob in order to see the Mona Lisa better.