I found a shiny Zigzagoon while training outside of Verdanturf Town. I was curious, so I caught it and took a peek at its summary. My friend at the time was watching me play and he pointed out, "Oh, you need to release that Pokémon! That star there means it's glitched and it'll delete your entire game!"
I had over 200 hours in Ruby, so of course I ran to the Pokémon Center immediately and released it. About a year later I discovered what shiny Pokémon were and how rare they are. I was so mad at my friend for the longest time. XD