The "!1" Phenomenon is a well-known but sparsely documented typo that is commonly found in online conversations. In many cases, a string of exclamation marks followed by "1" can be read as a careless typo, though it has been increasingly used with intention to express a sense of urgency or excitement. It is considered part of leetspeak, an alternative alphabet for the English-speaking internet users.
While he configuration of QWERTY keyboard layout varies across different language zones, an exclamation point is almost always invoked by holding down the shift key and pressing the digit / symbol key (1/!). As a result, the erroneous input of "1" after a string of exclamation points became a common typo in online chat, especially when typing in haste.
The typo gradually became associated with leetspeak in the late 1990s with the introduction of real-time online multiplayer games where punctual grammar leaves the gamer vulnerable to attack from the opponents, according to the academic research paper "Game Geek’s Goss: Linguistic Creativity In Young Males Within An Online University Forum" by the Australian new media scholar Katherine Blashki in November 2005.
The first UrbanDictionary entry defining the term was submitted on August 11th, 2003, which attributed the typo and over-exclaiming to carelessness of the typist.
!!!!1: Element of punctuation used by morons in place of the period, the full stop, that little dot near the L key. Note: one exclamation point is usually one too many. If you do plan to use more, please take care that you retain muscle control over the finger holding down the right-hand shift key.
Sometime in the early 2000s, some Internet users began invoking the typo as an identifier of Internet elitism, similar to the ironic usage of teh or pwned. The intentional usage of the typo was also suggested in another UrbanDictionary entry submitted on December 28th, 2004:
One: l33tsp33k replacement for the exclamation mark. Originates to the common typo in which a "1" is typed instead of an exclamation mark, as a result of the shift key not being held down. This evolved into the current derivative where the term "one" is fully typed.
The "1!" phenomenon has been frequently referenced in the machinima video series Arby n' The Chief, mainly associated with the protagonist Master Chief.
The typo is most commonly iterated as a string of exclamation points postfixed with one or more "1" at the end:
"I DON’T BELIEVE IT!!!!!!!!!!11111"
Occasionally, the postfix "1" may be spelled out in letters ("one") for humorous effect. In cases of extreme sarcasm, other numbers or prerequisite keys like "shift" are used alternately with "one."
A similar style of typo has been found in other sentence structures as well, such as substituting question marks with slashes ("/) or backslashes ("\") in interrogative punctuations.
"ARE YOU JOKING????///"
Depending on the layout of QWERTY keyboard, other characters adjacent to the numeric "1" key have been incorporated as well, including § (section), ~ (tilde) and @ (ampersat) keys. In the most extreme or urgency cases, a random jumble of non-alphabetical characters is used to convey a sense of chaos.
 Australian Journal of Emerging Technologies and Society – Game Geek’s Goss: Linguistic Creativity In Young Males Within An Online University Forum
 Two Hour Blogger – 10 Painfully Popular Typos Your Competition Can’t Wait to See You Make
 PurseBlog Forum- What Does This Mean When Someone Writes ….!!!!!!!11111111