Even seasoned travelers do dumb things. If I'm honest, I'm guilty of some of these so let's run through this and see how well you do.
Taking pictures of everything.
If you take pictures of everything you see on vacation, you're missing out. Live in the moment, take it all in and not from the other side of your camera lens. Who needs 25 different shots of the Eiffel Tower? And look at the time you've spent taking them. I'm guessing the people you're traveling with don't appreciate it either. Take your picture and put the camera down.
Eating only what you eat at home
Okay, I'll never eat Vegemite no matter how many times I go to Australia. But I'll try the local specialty if it just looks and smells good. Eating a Burger King on the Champs Elysees was not an unforgettable experience, but having fresh made pasta with sea urchin in Sorrento was. . You've already spent a fortune to fly miles away from your favorite diner, so give the wienerschnitzel a try. If you don't like it, there's a story.
Breaking the law
Once a taxi driver in Rome made 3 stops on the way to the airport to deliver a package, get gas and pick up an envelope and kept the meter running the whole time. When we finally got to the airport we paid him what we thought we owed him not what was on the meter and started walking into the terminal. He called a policeman over and after giving him our side of the story the officer told us to catch our flight. If the police hadn't seen it our way, we would have paid the driver in a New York minute rather than miss our flight and get in a "principal of the thing" argument. Obey the laws, don't take a chance on missing a minute of your vacation defendinig your right to start an argument, or driving too fast. Being an American abroad, you've already got one strike against you.
Expecting every shop to take credit cards
A lot of people will tell you that plastic is accepted everywhere. Well let me tell you it isn't. In some places it isn't even practical. Shops have to pay fees to take credit cards and often you get a better deal if you pay cash. I'm not talking about a big item, if you're buying a crystal chandelier in the Czech Republic, ONLY pay with a credit card. But if you're buying puka shell necklaces in Thailand bring cash. Part B Don't assume everyone wants US dollars. In some cases it costs a lot to exchange them for the local currency and for a small amount it may not be worth it. You're in a foreign country, carry some local cash.
Complaining about how different everything is
Don't go to Switzerland if you're traveling with a limited budget. It's expensive. Don't complain about being ripped off if you left a tip AND THEN found out the tip was included in the bill. Pay attention. If you're planning a night of clubbing, ask the locals when things get going, it might be midnight before the party starts. We know it's not like this at home, that's why we travel. When in doubt ask at the front desk of your hotel, it can save you some grief.
Ever been in Amsterdam where riding a bicycle is a real form of transportation? Watch where you're going and don't stop suddenly. If everyone in the crosswalk is running, my advice to you, start running too. Follow the lead when you're out exploring a new place. It's much safer. Oh, and forgo that perfect picture taken from the middle of the street.