2 1/2 days on a paintball trip with some friends. I was stomping through the woods alone during one game and experienced what I know is micro sleep, where your mind sleeps, but your eyes are open and your body keeps doing the simple things it was in the midst of, walking in my case. I "woke up" after walking straight into a small sinkhole.
Another time I went 2 days at a LARP event, which was almost worse since you are not only sleep deprived, but physically exhausting yourself as well. I slept 24 hrs after that.
I have a strange condition where I only ever clench my teeth when I sleep on an airplane. I now go without sleep, or if I must, discreetly put in and take out a mouth guard in the lavatory.