Mostly when I was young:
-in spite of suffering some horrendous bullying during elementary and middle school, I was actually bullying another kid at one point in middle school. A teacher who knew my history of being bullied caught me in the act, and (among other things) calmly said to me, “you know, there are a lot of people who think you aren’t like that.” I saw the hypocrisy of what I was doing and felt pretty bad about it; never did it again.
I killed some small animals with a BB gun.
I stole from my employer. Got caught, forced to pay it back. They didn’t prosecute, and in a further act of mercy, they gave me an opportunity to quit, rather than firing me; that way whenever a future job application asked “have you ever been fired from a job,” I could truthfully answer no.
Vandalism. Smashed a couple of garden gnomes, took out a streetlight or two with a well-thrown rock.
Once while backpacking with my family in Yosemite I saw a deerfly land on my mom’s hand. She didn’t notice it, and although I knew it was going to bite her, I didn’t say anything. Yup, after a second or two it gave her a painful bite. I immediately felt bad for not warning her, and to this day I still don’t know why I didn’t say a goddam thing.
Now that I’m 40, it’s hard to believe I ever had a mindset that could have done all that stuff.