Get upset when waiters, merchants, etc don't say what you would expect in America.

Expect everyone to speak English.

Quite frankly, it's rude to expect a non-English speaking country to be filled with English speakers. Be courteous enough to at least learn simple phrases and small talk.

Let anything get you down.

Be in a good mood, it's a vacation! You're getting an experience many people die without! Don't let anything get to you and ruin your trip.

Complain about the price of items.

Whether you're out to eat, or in a market or shop, don't complain about prices. You knew before you left that you would be spending money, and if you didn't do research about costs of where you are going then it is on you for not knowing what to expect. Many small shops are a family's livelihood. If you wouldn't accept lower than you are already paid at work, then you should understand.

Spend the entire trip on your phone.

Whether you're recording the experience for Snapchat, or just texting people that aren't there... don't. Live in the moment! Take photos sparingly, and tell your friends you'll talk when you're back! I cannot stress enough how lucky you are to be experiencing what you are alone, so there's no reason to miss things solely because you needed the perfect shot for your Instagram!

Talk only about your culture with the locals.

You're here to experience THEIR culture, not the other way around.

Disrespect any cultural customs.

Don't ever tell someone, "No, that's not how we do it where I'm from" and then refuse to do what they are asking of you to respect their culture. Do some research beforehand, if a culture takes off their shoes before entering a home, be sure to do so. If it is considered rude to do anything you'd normally do in American, try to do it the way of the culture you're immersing yourself in.

Go in blind.

I've said this in a few points above, but I really cannot stress it enough. Do research. Learn about the customs and practices of the culture you are going to be experiencing. Know about how much money you will need to plan on spending, know what you will need while there (plug adapters, passport info, etc). Never go in completely blind of what you're getting yourself into. There are millions of books, websites, videos, etc that will help you tremendously.

Give up opportunities while there.

Take every chance you can get to experience the most. Yes, you will be tired afterwards, and it probably won't feel like a vacation similar to one where you could be refreshed and renewed, but it is ridiculous not to take every possible opportunity to experience every part of a culture you've never been to before (or have been to and haven't experienced bits of yet).

Brag when you get back.

Don't be a dick. There is no reason to brag to others who weren't as lucky as you about your trip. Instead, educate others on the experiences you had. Tell people stories from your trip without being cocky about the fact that you got to go and they didn't.