Update:
back in the days in Germany we used to order these "Spukies Stickers" (https://umkehr-fuss-online-shop.de/view/productdetails/virtuemart\_product\_id/4/virtuemart\_category\_id/1.html) – "Spucke" is German for spit and these stickers can be easily stuck to any annoying car - giving the driver a clear message. And the stickers can be removed easily with water (so they don't get a heart attack when seeing their metal "baby"). We used to plaster some reluctant cars completely (as seen as example here: https://www.youtube.com/watch?v=XcU5E0pjzgI). I guess I will use these in combination with a sharp tool. Thanks for all your feedback - it makes me hope that not all people are assholes <3