Isn't particulary interesting, but when i first played with my sister (I looked up to her as a guitar player and my sis - never taught me anything, i just tried to do what she was doing) that was pretty cool.
Playing in front of the whole school (a fair few years ago mind) filling in for someone, they asked me to learn bass for it, and i did, and we rocked, played sepultura's "Refuse/Resist".
And another one would be playing in a local club with a comedy band, jammed packed and everyone loving it and dancing like 'tards