What did you do about the most difficult person you have dealt with face to face?

It depends on what you mean with difficult. 

Any way, I once got a job as a manager for a sales department where there was a guy (senior) who believed that he deserved to get promoted to this position. So from day1 he started to work against just to make me fail and prove to the management that he is better. Talking didn't help.  I tried to understand him and could see his strengths and weaknesses. So I gave him what he really wanted: Authority. I gave him more authority than he can handle and where he could identify his strengths and weaknesses. He made many (management) mistakes that made him realize the reason of not being promoted. He changed his attitude towards my team and me and became very cooperative. 

Dealing with people usually has two consequences:1. Either you both agree, or2. You don't agree.

However it depends on the situation you are dealing about and on your personalities, but if you have a difficult person try to:

1. Understand his or her difficulty.

2. Try to control yourself.

3 Try to offer or agree with him or her, if you cannot it is better to avoid dealing with them!

Piece of cake.

Simply, by using the key of success for handling the person which are difficult to face,   POLITENESS and follow up his desire, if it is reasonably practicable.

Nothing. ±++++++++++++++±+++++++++

involve the authorities above me e.g my supervising officer

Better to be Silent, than answer to the Ignorant --- !

I try to avoid, as much , as possible.

i try to take it out of his team  and put it under look   

To deal with such a client solve the problem in an ethical way if require we may look at by passing the process laid down but not before analyzing the risk involved. Deailing has to be diplomatic that it should meet the interset of both the parties

deal difficult person only with sweet smile and support  positively what he say but do which is right 

If I hv choice,would definately like to change him,as I believe that wasting your time and energy with such co worker is of no use for organization and me both.But if he is in superior position,patience and running proper professional procedures definitively will help to make a better professional relations and team work.