I've been working with Brits, Canadians, and Aussies for so long that I don't pay too much attention to our language differences any more. I had one colleague from Liverpool who used to get upset when I asked, "What's up?" when he called me. I meant, "What's happening?", and he understood, "What's wrong?" One British expression I had trouble with years ago was "boffin" (expert), which is what I'd call a "nerd". There's also "dole" (welfare). Not to mention the different interpretations of "tea".