Belgium: Don’t compliment them on anything. They’ll spend the next half hour bringing themselves down and assure you everything and everyone elsewhere is better.
Norway: Don’t sit next to people you don’t know on the bus.
Actually, let’s change that. Don’t interact with strangers unless it’s absolutely necessary
France: When on the Paris metro, saying a word or even showing a glimpse of emotion= instant French Death Glare
Ireland calling: Always stand your round. People will practically fight each other to be the one to buy the next round of drinks. They will tell you to put your wallet away. Do not listen to them. If you don’t stand your round you may as well call their mother a bitch and shag their wife in front of them, because that is how much of a prick they’ll think you are. Also don’t ever try to do an Irish accent. The major problem is there’s no such thing. There’s a Dublin/Cork/Belfast/etc accent. Try to amalgamate them in to an “Irish” accent and you will sound like a Leprechaun. A leprechaun that’s shit at doing accents.
From some Italian friends: Don’t lose your receipts. Counterfeiting is a problem, but so is corruption. If you buy a fake piece of shit and don’t have a receipt to prove you got scammed, the police will give you a hard time.
Turkey: Take off your shoes when you enter the house unless the host really, really expressively states you can leave them on.
Don’t refuse the tea. It’s rude.
Wales: Don’t refer to us as English. Ever. Ever.
When in America, never, ever touch other people’s children, especially if you are a stranger to them.
I took a bunch of Argentinian friends to a mall once and they were patting little kids on the head, which is common in their country. We almost got arrested.