A joke? Hm. All my jokes are usually just things I notice that don't make any sense to me.
As a kid I used to love putting PS at the end of notes or letters I wrote. Because it was like that extra secret you had to tell them "PS- I just robbed a bank. Don't tell anyone. I'm a bajillionaire. No you can't have any money." But then you'd actually forget to put something so you'd write PS and actually write something important "PS - I ran over your dog. I'm sorry. Please forgive me." And then the secret was lost, completely- so I would always add something else, and I always thought it would just be P-S-S. And then one day I was thinking about it, and someone said "You know PS stands for 'Post Signature' right?" and so I did the math, carried the 2s and the 20s, and figured...I was writing Post Signature Signature every time. I should not have left a secret, I should have been signing my name again. That's a Post Signature Signature, signing your name after the PS. I realized then that the correct term, is PPS- because it's after the PS. It's a Post Post Signature. So now I can gladly write after a nice thank you letter: PS - I think I gave you some type of sexual disease last night. I'm not sure which. You should get checked out. PPS - Please also tell your sister to get checked out. And don't expect a phone call. Not because I don't want to talk, it's just really awkward.
And then if I really felt the need, PPPS - I didn't sleep with your sister, by the way. I think she may have just gotten it from the toilet. I forgot to wipe it down when I was done, and there may have been something left. Really sorry about that.