Mine happened today in the morning...
So I finally decided to fight the E4 in Platinum, I made it to Cynthia, had no real items besides a bunch of MooMoo milks and one full restore. So I saved, fought her, got slaughtered, repeated the process like five times. Finally I got past her Garchomp and she sends out Lucario, which is much more annoying than Chomp. He kills my Giratina and Empoleon and Gliscor and I lose again. I decide to teach Giratina Psychic but I forget to save... so then I fight her, Garchomp kills me since I didn't get as lucky as last time. So then, I start again, and I think "Ehh screw this, after this round I'll just save after she beats me so that I can start fresh and gain a few levels or something...", and I decide to not teach Giratina Psychic again or teach Avalanche to Empoleon. and then... it happens. I manage to slaughter Garchomp and that portal thing I can't remember, and then she sends out Lucario... I forgot to put Psychic, and Lucario slaughtered me. I hated myself after.