If the cosmic joke is that we struggle all our life just to die at the end, then how else to survive but to laugh at the ridiculousness of it all. I think that is the main one. We are not Adult Mayflies that live about a day but it is a good exercise to think like one once in a while.
Because the field is so large, i guess there are any number of what could be labelled as 'the cosmic joke. ' Don't think the field is that large cuz we always really only have a human centric view to things. I suppose one could do some psychedelics and hang out with a May Fly. For a short period.