I'm not sure it was the worst, but it was definitely the most embarrassing. I cleaned my chain with gas on a Saturday, and let it dry, but forgot to oil it. As soon as I started out on the race Sunday, I knew what had happened, but there was nothing to do but keep going.
Lap after lap I rode around, squeaking and squealing...
Reeet-reeet-reeet-reeet-reeet-reeet....