There's a family systems theory of addiction that names several archetypes that family members of addicts fall into. One of these is the class clown type (the mascot). They learn joke to ease tension from a fucked up family but they are part of that family too and have their own scars that they'll try to hide (not to be sneaky, but for the same reason they joke all the time - so as not to upset anyone). Obvi this doesn't describe every jokster but I wonder if this is what you're seeing