Let's suppose somebody important, but you don't know him/her well (your boss, co-workers) are trying to tell you some joke, but you know it, or it is not a good one, or not which would make you laugh. What would you do? Force some laugh or just be silent, or ... ? With friends it is easier, enought to say "haha" that somebody was trying to be witty or so... Perhaps "Work laugh" from Friends? http://youtube.com/watch?v=Agb8h0fGlVw