In my case, (not counting yanking a friend away from a car that sped through a zebra crossing, and pushing the speeding car as part of it) - probably one of 2 cases:
- I almost squished my whole family, myself included under a giant glass mirror. I was about 6, and my parents bedroom had a huge (~ 2.5 by 4 meters) glass mirror with a heavy back leaning on the wall in front of the bed. Whilst the whole family was having breakfast in bed, I toddled over and pushed it. My goal at the time was to do so jokingly, since I had no idea what the momentum and weight of something that size would be. Fortunately, it tipped over and smashed without falling atop the bed and pancaking my family, or myself (I was right by it, but stood to the side).
- In a mountain hiking expedition by some ice caves, we set off a rock fall, including a (in my memory at least) goddamn Indiana Jones sized boulder. We were in a narrow, icy pass. Fortunately, the guide with us shoved us to the side so the rolling stones passed by us. Very close to us, given that as the outermost person, it grazed him, and we had to rush him to the hospital sharpish from there.