“You pay that much for your cocaine?! Hey, fly yourself down to Cartagena, Columbia, and you can buy a pound of the stuff for a fraction of the price you would have to pay here! Fly yourself home, and you’re good to go!” 
San Francisco makes a great day trip from Los Angeles, and vise versa. They’re in the same state, after all, so they can’t be that far apart.
If you talk to a New Zealand police officer, remind them of your American Constitutional Rights.*
*My wife did this when her cousin, a citizen of New Zealand, was stopped at a DUI checkpoint after we attended the harness races at Christchurch Downs. The officer had a good laugh about it as he reminder her that she was in New Zealand, not the US.
Every American dreams of taking a trip to romantic Paris someday, and enjoying the historic sights and wonderful food. One useful tip for the tourist is to know that the French have great disdain for their own language, so all of them have mastered English which they greatly prefer. Unfortunately due to some congenital defect they are all hard of hearing. So the correct way to communicate with a Frenchman is to talk to him VERY LOUDLY in English while gesticulating wildly. They appreciate this effort to speak to them on their own terms and this will get you the best service in restaurants.
Keep in mind, however, that tradition has retained the use of French in matters of cuisine, so you should learn some handy phrases which you can casually use in restaurants to show your sophistication. A very useful one to remember for use in top Michelin-starred restaurants is “Vous appelez cela une portion? Il ne suffit pas d’appâter un piège à souris” (“You call that a serving? It’s not enough to bait a mousetrap!”).
They also appreciate the sophisticated well-traveled critic, so be sure to tell them how much better everything is back home. For example, they will enjoy being informed that Kansas City has more boulevards than Paris, and, some have claimed, more fountains than Rome (a useful fact to bring up with the Italians). This sort of savoir-faire is sure to create a truly memorable trip.
The French also enjoy being reminded that their language was of great prestige and importance in the distant past. Tell them so. “Il y avait un temps, d’autrefois, quand le francais etait une langue tres importante et prestigieuse.”
Conversely, always try out your high school French while traveling through the US. Locals will enjoy trying to expand their repertoire (See, always learning!) of another language besides Spanish and will likely invite you home for a meal and a beer! The exception is Louisiana where they prefer German.
Also, while in Spain or Italy feel free to substitute the words from one into the other as they are identical. Make sure to point this out as much as possible.
And go ahead and park your car right up next to the water line and go for a walk. The ocean is really no different from a lake. Tides do happen occasionally but are rare.
For Europeans travelling to the flyover country in the United States, Americans understand that service levels have fallen in the recent years and we have become lazy and slothful because of our copious consumption of alcohol, fast food, and chewing tobacco. We like to be reminded from time to time that YOU are paying for services and should only demand the best.
For example, if you stop at a Quality Inn on a rural interstate outside of Chillicothe, OH at 9pm, you should demand to be treated like the foreign dignitary that you are. Very haughtily ask for a porter to unload your baggage and carry it to your room. Hand him a mound of clothing and demand that the valet have it dry cleaned for you by 6 am. Ask to see the room service menu. When shown the items in the vending machine, remind the American that these items are why Americans are so fat and lazy. This will encourage the desk clerk to reform his lifestyle and begin eating healthy.
Although you will not receive the service that you deserve, you will have at least taken a small step towards restoring the American “can do” spirit, and help to bring the United States into the first world. The staff will not appreciate your corrective gestures, but a follow up call to the corporate offices, complaining loudly, will get you discounts and coupons for further stays.
We liberal Bay Area Californians always welcome a variety of viewpoints. So the next time you visit, take a hint from this gentleman’s opinion of this place and let it inspire you to a similar speech as you make the rounds in Berkeley or San Francisco:
“Fuck this place, goddamn liberal fucks,
Eight guns out here somewhere as it is.
Fucking weirdos, probably driving around in fucking Hyundais, fucking roads and shit that go slow as fuck. You don’t have balls unless you’re fucking rolling coal, man. Goddamnit.”
Southwest Airline pilot, March 2021
When traveling in Ireland, make sure you where your Chicago Bears sweaters and ask if they have Coors Light available at every pub you enter.
Some of my wife’s relatives basically did this.
You don’t really need to take much water when hiking into the Grand Canyon. After all, it’s all down hill and there’s plenty of water at the bottom.
I’m told that when visiting Italy, ordering the national dish of “spaghetti and meatballs” is highly complimentary. Don’t forget to ask for extra sauce, like all locals do.
Bring a good sweater. Just like deep caves, the Grand Canyon is chilly at the bottom.
No need to rent a car in Southern California. We’ve spent billions on public transit over the past 3 decades and have a world-class subway/light rail system to show for it.
If you do decide to drive anyway and get pulled over, tell the officer you weren’t driving, you were traveling. They love that and will let you go on your way.
You’re sure to run into Hispanic people around here. Address them as “pendejo”; they’ll welcome you with great affection.
Everyone knows Taco Bell is fake Mexican food. Instead, go to Del Taco - it’s got a Spanish word in the name so it’s gotta be authentic.
The smog in the atmosphere blocks UV rays, so there’s no need for sunscreen at the beach.
Buy a map to the star’s homes. Climb over any gates and go ring their doorbells. You’ll see they’re just regular folks like you and me.
When using the subway system anywhere, it’s customary to stand across the entire escalator step, and make sure you stop and stand for a while when you get to the very top (or bottom) to get your bearings. Nevermind all of those people coming up behind you. The escalator will totally wait for you patiently.
Speaking of visiting Italy, when in Rome, don’t forget my tip above to mention (frequently) that Kansas City (the “City of Fountains”) is said to have more fountains than Rome. As with the French, Italians appreciate learning how much better things are “back home” than in their own countries. The purpose of constantly reminding them about the fountains is to encourage good-natured international rivalry. If Kansas City is going to loudly proclaim themselves the global leader in fountains, the residents of Rome may eventually be shamed into putting up signs at the Rome city limits reading “Benvenuto a Roma – Quasi tante fontane quante Kansas City” (“Welcome to Rome – Almost as many fountains as Kansas City”).
You can also remind them that while they had Michelangelo, who never really produced much of anything in the way of cartoon animation, Kansas City was where the timeless and iconic Mickey Mouse was created. Not by Walt Disney, as legend usually has it, but by Disney’s good friend and artist Ub Iwerks, in 1928, while both lived in Kansas City. The Italians are sure to be impressed and humbled by your extensive knowledge of the arts, and will gradually come to realize how wretchedly old and useless Rome is. If not, just tell them outright one evening over spaghetti and meatballs.
When visiting Stonehenge, don’t forget to bring spray paint so you can leave your mark on the ancient stones just like thousands of visitors do every year. Not to worry: it all gets cleaned up every morning! And don’t be fooled by those formidable-looking stones; they’re as light and easy-to-move as paper mâché!
And conversely, there’s no need to bring a sweater to California’s central coast. It’s sunny California after all. The Pacific Ocean is nice and warm. It never gets chilly after the sun sets.
(I made that mistake when I was still fairly new to California, which is why I own a sweatshirt from a souvenir shop in Morro Bay. The shop had the sweatshirts out in front, on the sidewalk, and the t-shirts all the way in the back, which makes me think that’s a common mistake for tourists to make.)
ETA: And this applies to San Francisco, too. Totally wear shorts and a t-shirt on the ferry ride to Alcatraz.
In Paris, if a stranger shows you a gold ring, buy it from him. It’s worth far more than you pay him.
The Washington State Ferries typically run behind schedule a bit, so don’t bother getting there on time. Pull up to the toll booth at the scheduled departure time, and you’ll be fine.