The 800 always seems to get some dramatic ones...
Had one teammate freshman year of high school who came through 400 in 59, looking amazingly smooth. Then probably 20 meters later you could tell it wouldn't end well, and he ran 88 for the second lap to finish in 2:27.
Another teammate ran a 4x8 relay leg at state our senior year, splitting 24/31/35/34 for a 2:04 ... which actually matched his open PR! That last 200 actually could have been way worse, had he not fought like crazy to stick with a couple guys who had passed him.
As far as I know, that was the last 800 either of them ever raced, since the first one only ran cross country after freshman year, and the second one didn't run in college.
My worst might have been an end-of-season 1500, where I was aiming for sub 4 (my season best/PR was 4:03 at the time). Came through 800 in 2:07, then struggled home with a last 700 of 2:10 for a 4:17.