What's the worst thing you've ever intentionally done? Do you regret it? Why/Why not?

Years ago (like 25 or so), I was out for a night with some friends at a bar in Toronto, and parked in a city parking lot across the street. Come out at about 2:00 AM to find some asshole parked his Jaguar right behind me (not a spot, the lot was full), completely blocking me in. Waited around for about 20 minutes hoping he had just parked to run somewhere quick but no dice. Ended up having to call the non-emergency line to get him towed, which took about 2 hours. I was beyond pissed, cuz I had a 45-min drive home to make, and had to work he next day. As we're killing time waiting, we go into the 7-11 down the block to get some snacks. I spotted some sugar in their household section and bought a bag, that I then poured into his gas tank. Only time I've ever done anything like that, but I was tired and angry at the total assholery of blocking someone in and wrecking their night. Was it a shitty thing to do? Yep, totally. Do I regret it? Nope.