Touch the guards. You can mess around in front of them and they’ll ignore you, but touch them and prepare for a world of hurt.
Talk with a fake English accent and say “pip pip!” and “cheerio!” a lot.
Call people “guvna.”
Don’t call the whole of the UK “England.”
Do not explain to us how you’re 17th generation Scottish/Irish/English/Spanish/Inuit/Ferret. It doesn’t matter and we don’t care.
Stop in the middle of any busy pavement and take pictures.
No peeing in the street unless you wish to be arrested.
I took £100 in Scottish money with me—most people looked at me like I had handed them a dead baby—do not use Scottish money.
If you’re in the south of England, don’t think we’re being rude if you try to spark up a conversation with a stranger in public and we look at you weird, it’s just not that common a thing to do.
Fuck around with chavs. They are nasty cunts and while you may be harder or tougher or stronger than them, they have a knife or 20 cousins with knives. They are our rednecks.
If you see aggressive-looking individuals wearing Nike hoodies, do not make eye contact and for the love of god don’t talk to them. They’re likely concealing a rusty kitchen knife and aren’t afraid to use it.
When someone asks “Alright?” or “How are you?” UNDER NO CIRCUMSTANCES ARE YOU TO REPLY NEGATIVELY. Lie if you have to, but unless you never want anyone to talk to you again reply with “Fine,” “Good thanks,” or anything similar.
Comment on the weather. Four hours will have passed before you realized that us Brits really do enjoy talking about the weather.
Don’t insist on cold beer; drink it warm and you’ll be glad that you did.
Order an “Irish car bomb” at an Irish pub.
Don’t comment on the dentistry unless you fancy needing some more of your own.
Use these or similar phrases:
… saved your ass in World War Two
… be speaking German if it wasn’t for us
Praise Margaret Thatcher when you’re in a low-income neighborhood.
Summary of most answers: Don’t be American.