A commonly used mockery of 1337 talkers, derived from the over-use of exclamation marks after a declaration. Since many people preferred using the Caps-Lock to the shift key, they would be unskilled with the shift key (if such a thing is possible) and it would end up coming out as !!!1!!!!111!!!! or things along that line. "Eleventy" or "Eleventy-one" refers to the groupings of ones located in an overly long string of exclamation marks.
"1337" person: So he's all like 'omg u ghey phag' so I say fucku bithc lolol!!1!!!1!!11!!!
Cynical bystander: Yeah, and then I was all like OMG!!!one!!!!eleventy-one!!