XDCOMPLETE
Egg-Cracker
Shiny Rhyhorn in the Safari Zone. Was before anybody had heard of Rhyperior as well, so it would have been nice to have a gen IV shiny right out the gate, but alas, it fled of course.
My very first shiny encounter was outside of Floaroma Town on Ruby. I was just running through the grass to train my team, and I ran into a shiny Zigzagoon. I had no idea why the color was different, so I caught it. Then I got the (stupid) idea that it was a glitched up Pokemon that could ruin my game, so I released it. Looking back, I can't help but facepalm.
Soon after this, though, I found and caught a shiny Linoone. Perhaps it came back to me after it evolved to give me a second chance?