I find the best solution just to walk to your car, smile at them, disengage the alarm, take a baseball bat or better yet, a steel pipe and chase and bash them till they bleed profusely. If done in proper manner, I estimate them to have approximately 5 minutes to get stitched up before they die of lack of blood.
I had a stupid fatherfucker sat on my bonet, then lifted one leg and rest his whole fucking leg while talking on the phone. I press the alarm and he didn't care. I shouted from inside a restaurant that is 1 shop lot away. I swear I wanted to take a knife from the shop's kitchen and slash open his throat, then reach my hand inside and break his spine. I don't care if this is too much but I hope one day, he saw his father doing that and his father got whacked up big time. Get to the root of the problem before attending to the problem itself.