Don't touch me, I'm British
Generalizations but reasonably accurate ones in my experience. I find it far easier to socialize and interact with strangers in the US than in the UK. There's a certain "shock" and disbelief that can appear in the eyes of a Briton if you randomly talk to them in public. I can't blame them though, I act exactly the same way until I leave its borders! Perhaps this is why so many Brits travel and move overseas ;-)An ancillary point that I've noticed over the years is the relative unpopularity of open social/discussion sites in the UK compared to the US. The UK is Facebook mad, of course, but doesn't really have a locally popular equivalent of Reddit, Hacker News, Digg, MetaFilter, etc. I wonder if the reduced desire to converse with random people has an effect in this scope too.