The "worst you've ever tanked" thread got me thinking. Tanking is another word for very bad positive splits, which tend to be a result of overambitious (read: suicidal) pacing.
So what about your most remarkable negative splits? Theoretically they should be easy: just jog the first mile of a 5K, then race. Has anybody ever deliberately done that?
I only have one good negative split story: 1:41/1:25 in my first marathon. I'd run a 1:20:38 half marathon one month earlier, so I was in shape, but I had a cold on race day. I almost DNS, then decided not to let all my training go to waste. So I went out easy and ran as I felt. By the 10-mile point I felt surprisingly good. So I decided to make a decisive break when I hit the halfway point and notch 6:30s for the rest of the race, if I was able to.
Strange feeling, at 13.1, to say, "Bye bye" and pick up your pace by a minute a mile. Great way to debut a marathon, in some ways. The wall wasn't remotely an issue.