I beg to disagree, you know instantly if you've been insulted by a Brit.
It's realtively easy to tell when a Brit is being condesceding and when they aren't.
I admit I exaggerated a bit.
I've only known a few people personally from Great Britain. The first was a family ironically celebrating America's 4th of July holiday with fireworks (which they called bangers), and introduced me to bangers and mash. Another was a fellow from Bristol who lived in my building a couple of years, and knew how to turn a phrase.
I'd love to visit the country as my ancestors came from there about 375 years ago departing from Devonshire, but I'll never have the money for a trip unless I start playing the lottery.