Looking for stories where you're character did something extreme enough to change their alignment. I'll start.

About 10 years ago in high school I was playing a bard (swashbuckler prestige class) on the more chaotic side of chaotic good (read: insane). My high-school bros and I were clearing out a grotto of undead when we stumbled upon a large underground city of orcs. We had tunneled into the back of a large hall with lots of orcish families eating at long tables and low fires burning in pits.

Immediately we had to start rolling to see if we were undetected by the dozens of orcs sitting around the room. We we're about to back up when one of the orc females with a child on her knee spots us. Not knowing what else to do, I pickup a long spear and throw it at her. I roll a natural 1 and the DM determines that the spear went straight through the orc toddler (this was a morbid group BTW). The orc mom in shock, I tumble over and grab the spear. At about the moment all the orcs in the room notice our presence and standup. I freak out and take the spear and tell the DM I need to end this before it gets out of control. Since I have crazy-high `initiative, I'm going to run around the room using my boots of speed and spear all the orc babies, making separate hit rolls and checks for each one. The DM is speechless, but he agrees. I get 8 orc babies on the spear before the first orc fighters turn. I face him with my 1d6-3 ocr-baby-kabob (DM ruled that baby corpses would blunt the damage), which now has a Disturbing Aura effect on the orcs. Eventually I end up killed by the mob. Once I'm resurrected, all the DM can say is "wow...that was fucked up", and rules that I am now chaotic evil.

tl;dr: In the heat of the moment I speared whole bunch of orc babies on a spear, then fought the orc fathers with the orc-kabob. Went from Chaotic Good to Chaotic Evil.