divided by a common language

over lunch earlier, an interesting topic came about trigerred by a malicious comment of a colleague to a colleague...

question: just when do we draw the line between "misuse of words", joke or abuse? which factors to consider when trying to communicate? seniority? authority? gender? culture? personality?

and then came a brilliant anecdote (dont know the reference though). UK and US are two nations divided by the English language as if to answer the previous question.

and then another question: does communication start with common language or the common need and want to communicate?