joke that doesnt end.

how many people have found themselves in one of these situations?
you start an inside joke with someone, now it isnt that funny outside of the context it was started in, and probably it was only funny in that specific moment. so the conversation ends and you figure it was over, the joke was dead, it had its moment but it had to die.
yet your friend apparently didnt understand that the joke died. so they continue to think its funny... and a couple of days later during another conversation they bring it up again. even though you dont think its funny anymore, and few jokes ever live for more than a few days, you play along listlessly. awkward moment aside you continue the conversation. inevitably they bring the joke back. now repetition does not equal funny (sometimes yes, but look at tom green and tell me it didnt get annoying after a while), yet your friend presses on with an ignorant grin plastered across their face.
does your friendship deserve this? should you outright mention that it wasnt funny, and in the process wound their precious psyche? or play along with lowering degrees of enthusiasm hoping that they eventually understand that it isnt funny anymore? are they dense? theres always the hope that it doesnt linger for too long, but it could become a black plague that follows your friendship along for days, weeks, months and most horribly, years.
maybe it is worth it to just kill the joke. that or dissapear for couple of days while they get it out of their system.
because that joke isnt funny anymore.