I think it also depends on the listener. For myself, most jokes are funny once and increasingly less so after that. Apparently, that's not true for everyone. I used to sing funny songs and had the same people showing up every week to hear us sing the same funny songs we sang the previous week and the week before that. As gnomad said, doing humor isn't easy; at least for me, it required lots of serious thought and practice beforehand. I must have been doing something right, though, since I regularly heard about what a great singer I was, and I'm really not -- I can't carry a tune in a bucket. It seems that funny songs can be successful even in the absence of actual musical skill. Presentation is everything when telling jokes, musical or otherwise.