Probably being accused of an incredible crime when I was a teenager.
Backstory: I'm nobodies favourite person. Especially in school; I was very poor, smelled like cigarrettes and quite awkward to be around in general, I don't blame anyone for any of the bullying but one thing affected me more than everything else. I don't want to go into detail about what rumour ended up burning my world down, but it was enough that the mere mention of it got me expelled and a police investigation was headed up against me.
Obviously, that investigation was fruitless as it was just rumours, however, it took nearly a year and I missed my GCSE exams (Without which you can't get a job essentially) by this point and there was no way another school would touch me.
Being accused like that, being treated like that, it broke me. I thought I was the lowest rung of society already, but how people acted after that rumour was spread, how even when I was proven innocent the police still had obvious disgust when looking at me. It taught me that no matter your circumstances it can be worse. People knew nothing of me but were glad to accept that I was a demon and they would not be dissuaded. It meant that preconceived notions are hard to sway and charisma and charm are the only currency that truly matter.
That arrest is still on my record and when I attempted to visit Canada recently it was flagged as a reason to deny me entry if I didn't submit proof that I was not convicted.
I am a different person today, being broken down like that meant I had to reassemble myself into a person I wanted to be. Being cast aside meant I lost my roots and could go anywhere (well, not Canada :P), learn anything, be anyone.
I invented myself out of that, to the person I would prefer to be.