from wglb in yesterday's discussion[1]: "In Soul of a New Machine, there is talk about the formation of Data General in 1969. The attorney advising the founders suggested that they set aside $1m each as part of any deal for the purpose of FU money. The usage may predate even that." (The book was published in 1981.)
That would definitely be before the first time I heard it.
My first recollection of it was one of Casey Kasem's tirades back in the 80's. I can't find the original on the web, but Bob and Tom spoofed it with "Mr Obvious - Too Hot for Radio" - http://www.youtube.com/watch?v=1Vobd2qDpzU
[1] http://news.ycombinator.com/item?id=1513390 ; Replies to the parent comment include other 1980s references to the term.