31337 was originally created by hackers who used UDP port 31337 to
hack into computers. 31337, when translated into letters, coincidentally became "eleet", which sounded very much
like "elite". And so they called themselves 31337, or elite hackers.
This "word" was later to be shortened to "1337", or "leet". The use of this word has spread to the gaming community, where many no-
life-still-thinking-they-are-cool people use it. It has also become a language, where symbols are used to resemble letters.
People who type in 1337 are usually "high ranked" people with no
life other than playing their favorite MMORPG.
They would say something
like:
OMFG!! 1 pwnt da n00b
bad so STFU NUB!!
Translation:
Oh, my fucking god! I owned the newbie
bad, so shut the fuck up noob!
This, as you can see, makes no sense. Except if it's to make fun of people to whom it does make sense.