I have travelled all over the US and the world for business and leisure. My wife and I lived/worked in the Czech Republic (Prague) for 2 years in 2010-2011. While we were there we travelled extensively in Europe, western, eastern and as far east as Turkey. While we lived in Prague, which is a beautiful city and a huge tourist destination, where the most "ugly" tourists I encountered were Brits, Russians and Chinese. In all my time there, on city streets, riding the excellent metro and public trans system, and going to all kinds of touristy and just regular places, I never encountered the ugly American type anywhere. Drunk and obnoxious Brits for sure, and unbelievably rude and loud Russians absolutely. Chinese tourists in huge gaggles that would knock you off the sidewalk ... check!
My brother and sister have lived in Europe for 30+ years each (UK/Scotland and Spain respectively). They both have hilarious stories about Germans on holiday who take over beach chairs/loungers and prime spots ... it's actually kind of a European meme.
Americans are hardly universally perfect at all, but there are plenty of other nationalities who have some pretty nasty public habits while travelling.