For millennials, like me: 1337 means "LEET" which is short for "Elite".
xkcd
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Sorry, what? I'm a millennial, this is common knowledge for anyone who played a videogame in the last quarter century.
I was going to say, I think the perpetuation of leetspeak and most of its use falls squarely into the millennial generation's early 90s into the early 2000s.
What the h311 is wrong with you? Us millennials invented 1337!
Nope. Source: am gen X.
Yep I think pops here has this one, us Millennials grew up with leet speak, it already was a thing in the 80s.
I'm confused as to where you fit in the Millennial demographic for you to have not known this already
Millenials pwnd the n00bs with the best of the genX back in the day, but I think leetspeak was a lot more niche than say 67 is, it was very gamercoded/nerdcoded when that wasn't cool.
Source: am millenial who had a leetspeak AIM handle back then
Ragebait. Millenials are like 40 and have back pain.
I know it just means you aren’t familiar with it but it’s funny you picked the millennial one as the one you had to explain to millennials.
0118 999 881 999 119 725 3
I think it's more of a 0118 999 88199 9119 725 3
Oh, that's easy to remember!

I was reading Wikipedia about the origins of 23 and came across this neat tidbit:
On the RMS Titanic there was a watertight door on E Deck numbered 23 which was informally called the "skidoo door" according to the testimony of the Chief Baker Charles John Joughin.
twennyone
You stoopid
Maybe not a teen thing, but among children I think "because 789" could bring 789 into the discussion.
Further cementing that there is an xkcd for everything.
Teens in different countries have different funny numbers too funny enough. There is a thing influencing multiple civilizations to do this.
31 is funny in Turkey.
If you're gonna include 23 skidoo... You should include being at sixes and sevens:
https://en.wikipedia.org/wiki/At_sixes_and_sevens
67... Is very very old British slang for wrecked/confused, at odds, or hysterical.
"I was all 6's and 7's"
I think some will still understand it, although I can't remember the last time I heard anyone use it.
1 hehe