It might not be possible to know everything that overseas citizens find offensive but the first bit of advice I'd offer is that IF you were only going to one or maybe two countries and staying for any reasonable length of time, get etiquette guidelines for that country. Especially for business travelers or those staying or meeting with home dwellers. In some Asian countries, not eating all the food prepared is an insult to the host - in others you are supposed to always LEAVE a small portion on your plate to indicate a hosts generosity. For reasons like this, travel etiquette is a minefield and the more you know, the better off you will be.
To avoid the "U.A." tag, learn some of the local language. Don't insist on everyone else understanding English. They may well know English yet not tell you if they sense you expect them to know your language but you can't even say "merci" back to them. Toward that end, don't always converse in English if you know any of the local language. Learn how to say: "I speak very little...." in whatever language is the norm for that country. If you were in a local cafe or pub/bar and made any friends, ask them "How do you say...?" and I suspect you will be a star since it shows a willingness to 'do as the romans do'. Practice learned phrases and words - it will help you down the road. People love to help others but they don't like being taken for granted.
To really get a flavor for local culture, avoid the Burger King/McDonalds routine. You can eat there when you go home. Go to local cafes and pubs, even if you can't speak the language. But don't sit down and ask them to make a Manhattan or Cosmopolitan unless you are in a fancy restaurant or bar. Get a beer (or a 'pint') or a 'scotch over' (preferably in their language) or something otherwise simple. They'll love you if you make it easy on them at least for the first order. After they see your tip, I'm sure they will be glad to make the fancier drinks. Learn the local 'bar games' like darts. If you ask them to show you 'how it's done', you'll probably have a friend forever. And if they invite you to play first, don't be an 'U.A.' - just get up and throw the dart through the window if you must but don't be rude and wave them off. Show the host country you are a sport and they will make your trip a memorable one.