In the old days, a friend of mine would carry some paper(?) stickers(?) (labels?) that said something like "I park like an asshole" and superglue it to one of the windows of someone parked like this.
If you wanted to be nicer, you could get some proper pre-printed stickers (most online print/sticker shops should have them) and place them. Wouldn't cause any damage but would maybe make them think about it a little bit.
I also saw a post recently where someone replaced all the tire valve caps with bright orange or pink little dick shaped caps. This would cause more inconvenience and embarrassment, but not be damaging or dangerous.
I knew a guy that had a roll of custom-printed "I park like a jackass" stickers. They weren't very large -- I think they were originaly labels for folders or something.
But they were on tamper-proof stickers, the kind that were metalic and broke into a bunch of tiny pieces when you tried to peel them off.
He'd slap two or three of them on the driver's side windshield and window out of the main line of sight, but you couldn't miss them when driving.
They're a pain in the ass to get off. I know, because he put one on my car that said, "I lick sweaty ballsacks".
Holy shit I just found penis tire caps on AliExpress, definitely buying some lol
Edit: I realized I don’t have the courage to actually do this to someone in public and risk getting caught, so I didn’t end up buying any, but they are readily available from your preferred discount app if anyone else wants to
Haha, nice! Here, I found the post, in the old "R" site. I try to avoid posting stuff from there, but this is in the interest of science: https://i.redd.it/idl8jj50fg6b1.jpg