I put a note on a crooked car at the library that messed up everyone else. I feel like a badass
Do you think people would appreciate you doing that?
A lot of the folks at the library would.
Trying to correct peoples bad parking behaviors might be useful. It could be seen as hurtful if your note was passive aggressive, there might be a reason they parked badly.
Maybe, but I'm now going to leave a note with insults directed to the owner to make them feel bad. I feel soooo good that I messed up another person's day.
It is good to follow traffic laws and park in the lines.  I think if you leave a hurtful not the person might start parking bad out of spite so it might help to have a bit of mercy.