The word droll means funny but in a sort of odd and weird sort of way.  For example, you would not say that it is droll when someone slips and falls and their food that they are carrying lands on their head.  It might be funny, but it's not droll.  Droll has a meaning that is more odd than this kind of humor is.

The best example of "droll" that I can think of comes from the famous "'Twas the Night Before Christmas" poem where it describes Santa Claus by saying

His eyes—how they twinkled! his dimples how merry!
His cheeks were like roses, his nose like a cherry!
His droll little mouth was drawn up like a bow
And the beard of his chin was as white as the snow;

As far as diplomats go, I suppose a diplomat could look droll though it would probably not help them because you would think diplomats should be dignified.