Ok... how do I say this carefully?
When you're in Eastern Europe (this isn't nearly as bad as in western Europe), just be carefully around gypsies. Most of the ones you see on the streets are probably harmless and just begging (or selling kids toys), but they are known to potentially get violent as well.
Also, I think you are not giving yourself enough time to actually explore these places. Now I haven't been to Europe since college, but I found that I needed around a week to explore one city to my liking. I understand if you want to go to as many places as possible, but you will likely be rushing and missing quite a few landmarks on the way.
Edit: Guy below made a good point - Europeans don't really like Americans personally (except for the British). So if you want (this is what I always do), simply get a Canadian pin or flag or whatever and put it somewhere were people can see. Everyone loves our country, so you should be treated much better if you do this.
Made a bet with LipeJJ and HylianYoshi that the XB1 will reach 30 million before Wii U reaches 15 million. Loser has to get avatar picked by winner for 6 months (or if I lose, either 6 months avatar control for both Lipe and Hylian, or my patrick avatar comes back forever).