@Simon: Even though it may become more casual and less nitpicking, it is better to know the proper usage, especially if your boss is a pedantic grammarian. I am very careless when writing comments. I simply don't check what I wrote, very unlike essays which I have to go through drafts and a proof reader. It is so much easier to correct others than one's own. "Words you use DEFINE how others..." we all make such mistakes all the time :(

June: I agree with June. This is a word that people use less and less. So for the purposes of this short question, WHO is acceptable and cannot be misinterpreted any other way. Jeff: Some corrections to your comment above: (1) "If I am speaking to my boss, I better watch the language I USED" should be "If I am..watch the language I USE" (2) "Words you use IS DEFINED how others view you in social life" should be "Words you use DEFINES how others.." Thank you for putting effort to make corrections on my Chinese post. I will continue to write more for you to read :)

It really depends on WHOM you are speaking to. I won't waste my time debating the correctness of the usage with a farmer LOL. If I am speaking to my boss, I better watch the language I used. Words you use is defined how others view you in social life. Speak like a farmer and you will become and remain one. Speak and write with flair and eloquence, people will view you in high esteem.

I understand it should be 'whom' from the grammar point of view. Have said that, we know things change all the time and language is one of these things. So 'who' is acceptable in this sentence. It seems that 'whom' is used less and less.