When two of your friends have sex in the same room as you and don't warn you or ask you if it's okay.
Its called being 9/11ed because you'll never forget.
a: "Stacy and Tod totally 9/11ed me last night."
b: "Oh yeah they tend to 9/11 a lot of people."
When you're feeling super good, like you are on top of the world, and some force, probably a stupid bitch, completely makes you do a 180 and start hatin' life.
Like The World Trade Center on 9/11/01. Thus, the term 9/11ed.
You are walking through Wal-Mart and you see a girl you know and you enthusiastically say hi and all you get is a very under-enthusiastic hello.
The conversation amongst you and you're friends might go something like:
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).