Created November 24, 2009 by a DJ from Memphis, TN, called "Record Player". Used on Facebook as an example of abbreviations that could be typed to show amusement instead of the overused "LOL".
Fah! Can be used simply as a response in the same manner as LOL.
(9:34:28 AM) GM: lol
(9:34:28 AM) CT: way to multi-task
(9:35:22 AM) GM: sigh......I wish I was there to laugh and mock.
(9:38:20 AM) CT: ur terrible...
(9:38:28 AM) CT: of course... only u...
(9:42:35 AM) CT: FAH