OK backwards. Originally from Short Circuit 2 (1988), K.O. Derf is OK Fred backwards. Became more common with the rise of chatrooms and IM with people who can't or don't waste time trying to type well.
fred: are you ok?
#5: Functioning 100%. Perfectly K.O., Derf!
fred: it's fred
#5: That's what i said, Derf!
im user 1: i gtg
im user 2: wait bring that cd tomorrow
im user 1: ko durf ttyl