I probably was bu but it was heat of the moment and it's not like ive damaged his car. It was just gently placed in the plastic fan blade type thing, could be easily pulled out.
He had parked right behind me so that I couldn't open my boot, he was touching my tow bar. Normally I would hang the poo bag on the tow bar till I get home but I couldn't reach it. Couldn't get the dog in the boot. More importantly I couldn't reverse out the space like I was planning to and had to go forwards over a 45degree slope/bank and was worried for a minute the car was going to topple over.
I hope it made his car smell of poo on the way home!