As Oscar Wilde put it, the United States and the United Kingdom are "two countries divided by a common language." While both nations speak English, there are regional differences in how words are spelled that can bamboozle even the most enthusiastic pond-hopper. Many a business relationship, friendship and romance have been jeopardized by not understanding the correct idiom, misusing a word, or putting the date the "wrong" way round. Spelling is yet another minefield when it comes to communicating, with each nation firmly convinced that their way of doing it is the right one.
Of course, you would never be befuddled by something so simple as talking British - because either you are British or you've been there so many times (or simply watched so much "Downton Abbey") that you're essentially an honorary Brit. You know when to use an "s" instead of a "z," when to keep or dump a letter "u," and whether you need a single or a double "l." You can code-switch between these two great nations' dictionaries with the agility of a truly international traveler (or perhaps, traveller).
Still, since most people can't keep up with your expertise, it's very rare that you get to show it off - so click on through and prove your British cred once and for all!