I've lost a few games over the years.
Blue, Silver and Trading Card Game I actually lost. Dunno how, they were in my bag (that held cartidges, my GBC magnefier, (it had a light, night time playing with no lamp *hehe*) my exchange cable, and the GBC power cable) and they just must off climbed out and walked off. Strange.
Red was stolen from me, I lent it to a, then (primary(UK)/elementary(US)) friend, he then tore of the sticker on it, and claimed it as his own, I even told the teacher and headmaster, but because he ripped of the sticker I couldnt prove it was mine, BUT IT WAS!!!!
And (although not Pokémon related) I lost my, then newish, DSlite and all 7 games. By lost I mean left on a coach, I just forgot to pick up the little holder there where in when I got off. (I know I have to have something to carry portable cosoles and games around in)
I never played Gen III
On a lighter note:
Gold, Cyristal and Yellow (my first EVER game) I gave to my brother many years back, along with the bag I mention before and all 400+ cards I had at the time. He still has them, plus more, games and TGC.