What's the darkest thing you've done which no one knows about?

When I was 16, I had this friend, let’s call him Sam. We weren’t super close, more like those friends who hang out because they’re in the same group, but I always thought he was a bit... off. He had these sudden bursts of anger, really dark humor that made people uncomfortable, and he’d sometimes just stare at people for way too long. Anyway, one night we were hanging out in this abandoned construction site near our neighborhood — this was our dumb idea of fun back then, climbing around, breaking shit, being edgy teens. I remember Sam picked up this small bird, I think it had a broken wing, and started just... playing with it. Like, tossing it gently in the air, laughing at how it couldn’t fly. Then he snapped its neck. Just like that. No hesitation, no remorse. I still remember the sound. I froze. I didn’t know what to do. He laughed and said, “Relax, it was gonna die anyway. I did it a favor.” But I couldn’t look at him the same after that. Later that week, I found his Instagram account where he posted drawings — really violent, disturbing shit. And captions like “someday I’ll stop imagining and start doing.” That line stuck with me. Here’s where the “darkest thing” part comes in. I wrote an anonymous tip to our school counselor. I didn’t say who I was, I just wrote that Sam might be dangerous, that he was killing animals and posting violent stuff online. A few weeks later, Sam stopped coming to school. I heard his parents sent him to some kind of inpatient psych facility. No one ever found out it was me. Our group just kinda moved on, barely mentioned him again. Sometimes I wonder if I overreacted. If maybe he was just a weird, edgy kid going through shit. Or maybe I actually stopped something worse from happening. I’ll never know. But sometimes I still feel guilty. Like I destroyed his life for a bird. Like I played God. That’s the darkest thing I’ve done. And I still don’t know if I did the right thing.