In negative sentence expressing that you don't quite get the reference of the pun but you like puns.
In positive sentence it means you understand the pun and want to top it with other one.
A: I'm reading a book about anti-gravity. It's impossible to put down.
B: I don't punderstand.
A: (winks and point fingers at B)
When you have to pee in a movie but don’t want to miss anything, and must do the following mental equation: will the amount I have to pee cause enough discomfort to diminish my attention capacity for the remainder of the movie to an extent which is greater than the amount of the movie I would miss by making a mad dash to the restroom.
I saw Satantango last night, wonderful film but by the 5th hour I had to start doing pee calculus.
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).