In June of 2000, when I first came to England to meet Andrew, it also happened that my youngest brother's best friend and his wife were staying in a Canary Wharf flat their company was paying for. They were in England for six months to start a London branch of the U.S. company they worked for. I had been in England for about a month, got in touch with my brother's friend and his wife (Andy and Dina), and as they were in London, with no car, Andrew and I went there for a night out. After getting hopelessly lost, we made it to their place. (As far as London real estate goes, I can only imagine how expensive that flat would be: two bedrooms, with a balcony on the Thames, with the Millennium Dome directly opposite). Anyway, we were going to go out to dinner, but Andy said we should go to this pub (the ONLY pub) that was near where they lived. And so we did.
There were maybe 10 people there: it was early evening, football/soccer was on the TV, there was a dog hanging out with his owner, etc. A lazy pub afternoon. Loud classic Brit rock playing (Stones, Zeppelin, etc.). Andrew (my soon-to-be hub) insisted on going to the bar every time a round of drinks was due. My American friends and I were asking Andrew about the school system here, laughing about some old times we'd had in the States, etc., when Andrew pulled me toward him and whispered in my ear: "Whatever you do, do NOT bring up the British monarchy, even if it's for a laugh, DON'T cut on soccer hooligans--just trust me on this." I was bewildered and said okay (the Americans I was with were very smart, notoriously and bitingly sarcastic, but those subjects hadn't come up--Andrew was covering the bases.)
They had been there only two months, so didn't know what the politics of a pub could stand for. After we left there and went out for dinner, Andrew told Andy and his wife that their "local" was a BNP hangout. I asked him how he knew. He pointed out that, except for us, there were no women there, all the men had close-cropped or shaved heads, the English flag was hanging everywhere, while my friends and I were talking he'd overheard a couple of men at the bar saying something about "those *bleep*ing Americans" (not about us, but about something they'd heard on the news). It suddenly all made sense. Andrew's usually pretty introverted, but he insisted on going to the bar that day to get every round of drinks, because he didn't want the people at the bar to hear an American accent. And that was the first time I'd ever even heard of the BNP, much less had an idea of what they might be about.
When he told Andy and Dina about it later, they were stunned. They attributed not getting beaten up before to the loud music in the place, because they'd been there before and had joked about football hooliganism with each other, etc. What it came down to was: How was an American to know?
I guess it would be similar to walking into a bar that, on the surface, seemed normal, but was really a KKK hangout.