I have good news, and bad news for my fellow Boomer (and their kin) out-of-country-travelers.
The good news: American tourism to other countries provides money and jobs to often struggling locals...yay us!
The bad news: the rest of the world thinks we're terrible travelers. It's so bad, in fact, that the term "Ugly American" has become shorthand for any of us who stick out (in ways we'll be going into) or do inadvertently rude things when vacationing in other countries.
...you don't have to be fluent in a country's native language in order to visit it—but at least make an effort to learn key phrases and words. Knowing how to say things like hello/goodbye, how to ask for directions, and how to say "Do you speak English?" in the local language can go a long way. American tourists are notorious for just talking louder in English when a nonspeaker doesn't understand, so don't do that. You can also use hand gestures, phrasebooks, or apps to get your point across.
To the rest of the world, everything's bigger in America, and that's not always good. It doesn't help the stereotype when Americans complain about small portion sizes while dining out abroad. Think of smaller portions as a way to sample more dishes or to reevaluate your own eating choices.
White sneakers, a fanny pack, a baseball cap. This uniform can make a tourist stand out—and not in a good way. Wear what's comfortable, but do make an effort to blend in with what the locals wear, especially when it comes to covering up in more modest countries.
Don't demand to know the price in American dollars. It's fine to do the math in your head or on a calculator, but don't ask a merchant how much their wares are in "real money." Get a rough idea of the conversion rate before you leave and do the mental math instead, or download a currency-converter app for your smartphone. You'll be shopping like a local in no time.
Ever heard a fellow American tourist brag about "how America does it" or say, "Well, back home, we …"? It's great to discuss cultural differences, but if you're pointing out customs that you think are flawed or not as good as "how we do it here," then you're missing out on the whole idea of travel.
You're traveling for a reason—to experience new things! So don't automatically seek out the nearest Starbucks when you're overseas. Sample the local restaurants as well as the cool fast-food chains that we don't have here. And don't squawk about amenities we take for granted (like air-conditioning or Western-style toilets) that aren't available everywhere; be prepared to adjust to a different standard of living temporarily.
This is another way Americans have a reputation for being "oversized" in other countries. Overpacking can be a clear indication of an American tourist, so don't struggle up the stairs of your hotel with a huge suitcase if you don't have to. Downsize to a backpack or small suitcase—if you run out of clothing, you can always go shopping while you're on vacation, and then you'll really look like you belong. Or, do laundry at a laundromat near your hotel—it's the perfect chance to mingle with locals.