Although I am not personally familiar with much of this, I have heard brief variations of them over the years.....but I was startled to see on late-night TV just a few days ago, an entire program devoted to 'contests' on this theme. There seemed to be 'topics' given by the MCs for the contestants to improvise on, as well as 'free-style' insults.
   I...ummmm... didn't watch long enough to gain many useful insights. Just a piece of culture that is beyond me.