Used to show extreme exclamation. On most keyboards, the '!' exclamation mark is the shift function of the '1' key.
Often, when typing many exclamation marks, some 1's would appear as a result of continuing to hit the '1' key after no longer pressing Shift. The result would look something like this: !!!111. This has morphed into the use of "!!!111oneone" to show extreme exclamation.
Holy !@#% this site is AWESOME!!!!111oneone.