I have some great stories about sounds that I originally used for one thing, then was able to completely change, and re-use as a completely different sound.
For example: I recently did a bunch of high speed (192kHz) recordings of shooting pennies out of a slingshot. I was able to use it as a ricochet sound for a bullet, and then I repurposed it as the sound of an airplane engine (not for an actual project, just to show someone that I could do it).
Anyone else have similar stories? Maybe some funny ones about using very unconventional sounds for something you'd never expect? (Wilhelm scream anyone? ;-) )