You should report them to whoever issues license plates there. They take this stuff seriously.
I don’t see a specific place to report an offensive plate, but I did send an email to the Indiana BMV. They review personalized plates and reject some, so this must have slipped past their radar.
https://www.in.gov/bmv/registration-plates/license-plates-overview/personalized-license-plates/
Or key the car, if you’re out of sight.
They shouldn’t do anything like that, or slash their tires, or put a brick through their windshield.
Potato in the exhaust is a classic.
I’d rather eat the potato, though.
Rutabega in the tailpipe.
Slap some bologna on to it.
Someone put a piece of American cheese on my exes car once. I thought it might be because of the pagan symbols on it. Took like five minutes to scrape and wipe it off, mostly because it slightly melted despite the low temperatures.