I encountered a shiny Whismur, and thought my game was cursed. I was convinced that if I caught it, everything in the game would turn shiny, including all the characters, buildings, scenery etc, and annoy me for the rest of my playing days. So I ran from it.
I was only 10, but it's still worthy of a facepalm.
I had a busload of Pokes and a lot of traded ones from Emeralds Safari Zone [GSC] and I also caught a shiny Golbat and raised it into a Pink Crobat that became a permanent part of my team...the started getting boring after a while...so I restarted...and that's when DP came [ i found out about migration] and I havent stopped kicking myself about it yet...this was on Ruby...
Going up against Wallace (Emerald) with a lv.80 Swampert and 5 lv.35 pokémon.