In the 70s I travelled a bit by way of thumb (hitchhiking). In one major North American city, I met some other young tourists from England. We were sitting at an outdoor cafe, when one of them casually asked me if I knew where he might pick up some fags.

Fortunately, I knew that 'fag' is British slang for cigarette, and by his body language (patting down his pockets) that cigarettes were in fact what he was asking about, but I also knew what connotations it had in the part of the US we were in, and that very few locals were likely to know what he meant. I apprised him of the other meaning, which he had never heard of, but was grateful I may have saved him some... misunderstandings.

"The United States and Great Britain are two countries separated by a common language." —George Bernard Shaw

"We have really everything in common with America nowadays, except, of course, language." —Oscar Wilde

http://en.wikiquote.org/wiki/English_language

(Personally, I would paraphrase the above quotes to include Australia, Canada, and other English-speaking places. I've spent several evenings into the wee hours discussing language differences with Canadian friends who live only 100 miles away...)

That incident—among others—have engendered in me a curiosity/interest in words, idioms and etymologies.

Doc