By that, I mean what's thing have you done that's the most likely for someone to react with "how the heck could you have done that on accident?"

My example: I successfully cooked a prime rib on accident. I was in charge of the house while everyone else was gone, and there was a prime rib slow-cooking in the oven. The problem was that a mist was coming out of the vents, and I didn't know it was normal. So I'd see the mist, turn off the oven, call my parents and grandfather, they would assure me it's normal, I'd turn the oven back on, and the cycle would continue because I don't risk that stuff. When they finally came home, we had the prime ribs for dinner, and the way I caused it to cook actually improved it. They bit out of it and immediately said "this is the best prime rib I've ever had". Thus I accidentally cooked a good prime rib. That's a positive experience anyways.

What some might say is my most profound negative example: There was a Minecraft level that was a replica of the whole nation of Denmark, and while the features that would allow it to otherwise be destroyed were disabled, I accidentally found the glitch that led to its demise and eventual conquest by America.