Short for Friday Night Frag Fest. Usually used in Quake3 with a full server.
You shoulda been in the FNFF, damn, I was on FIRE!
A funny peice of comedy used by Spaceghost on the Spaceghost Coast to Coast episde "Boo Boo Kitty"
"One, one is the lonliest number you'll ever do... boo boo, oh what a fine cat, what a lovely wife you would have made."