For the uninitiated, the most common expansion of PJ is a Poor Joke.
If you have been in the field long, of PJ-ing, you would know that PJ could also mean a Pleasant Joke, a Passable Joke, a Pathetic Joke, or even a Please Jump-outa-the-window signal!
There are variations too, Like DAJ - a Desperate Attempt at a Joke.
I felt like remembering the PJ's I used to write on the fly, in my previous company...
Q:How do you chase home a lazy diner?
A:Uto, and get an auto
(In my previous company, the beverages from the Nestle vending machine tasted much better than from the Lipton vending machine, so..)
Q:What is the difference between tea from the Nestle vending machine, and the Lipton vending machine?
A:One is Nestea, the other is Nasty.
Q:What do you call a pregnant South Indian?
A:A gravid dravid.