Calling someone by their first name

[StevieG]

Easy rule is to just keep things formal (Professor, Doctor, Sir, Mr. RunDownHouse'sGirlfiend'sSurname) in writing and especially spoken. Those that want you to use their first name will correct you.

As for the law clerk -- his reaction was out of line, but "your office" or something like it would have been better than "you guys" in that conversation.