The most recent significant blow-up has to be Naoko Takahashi.
All that she needed to do (November 2003, Tokyo) was win in about 2;24-2;25, 5 minutes slower than her PR of 2:19, and she would make the Olympic Team.
She went through the half in 1;10 and then ran the last 5km in about 21 minutes. She was passed by Elfenesh Alemu in the last 3km and ran 2;27.
She and her coach claimed that it was due to hot weather (it was unseasonably warm in Tokyo that day, about 70 degrees), but she's run 2;21 in Bangkok in 80 degree weather.
I was there, I saw her before the race, she did not eat much at all.
The whole thing cost her a return trip to the Olympics.
As for me, my best blowup, one that I still laugh about was in Hamburg in 2002.
I went through the half in 1;11, hurting badly, and then I had to take a truly enormous POOP at 25km. I wore the wrong shoes, a pair of Japanese style raceflats, and my feet were killing me by 14km.
I just kept on going, due to the great people of Hamburg, ended up finishing in 2;55, for a 2nd half split of 1;44!!!
Now I know how Oprah feels.
Jason