I have not encountered a shiny since Gen 2 Days....
The one Shiny I have seen was in Fire red but it was one of the Battle Tower trainer's Meowths
Although this is not something that happened to me personally, I would still count this as a "bad shiny experience"
A friend of mine was playing one of the Core Gen 3 Games (I can't remember which one of the top of my head) and managed to catch a shiny Electrike. His friend though it would be absolutely hilarious to rip the Gameboy out of his hands, and shut the game off before he had a chance to save it. He hasn't even encountered a Shiny since.