I'm an American living in the UK for *checks watch* about eight years now. Before I came I could manage Japanese and have since learned French, and yet I still haven't the faintest idea what on earth you people are trying to tell me half the time.
Best example was summed up by a nice Northern bloke who, on seeing my confusion with basically everything quipped, "America and Britain are two nations separated by a common tongue." Truer words were never spake. I think. Honestly, he was both British and Northern so it's entirely possible he said something entirely different.