Common typo among people who like to insert many exclamation points to the end of a sentence, caused by accidentally releasing the Shift key before the 1 key, and sending the message without previewing it to realize the typo had been made.

Often used on purpose to make fun of such accidents and the people who make them, or as part of leetspeak.

A similar but less-joked-about occurrence is the tendency to insert backslashes after a string of question marks.

Punctuation commonly used in l33tspeak that emerged from a typo.

When you copy and paste "!1!1!1!1!1!1!1!1!1!1" and go too far.

used at the end of an extremely sarastic statement

Used to make a sarcastic statement even more exaggerated.

Something that you out at the end of your sentence to be sarcastic

the repeated usage of 1!!11! indicates the sarcasm after a phrase, sentence, or word.
for example
-" i hate you for saying that!1!1!1"