Dropping food and juice in someone's car is completely unacceptable regardless of whether it's a BMW or not. Don't let them eat/drink in your car if they can't keep from making a mess.
Leaning on the car is a bit mild in my opinion, but that may be just because it's unavoidable -- if I park my car in the streets in NYC I will come back to find random strangers leaning on it like it's a tree or something. Last time it was these 3 teenagers who didn't even stop when I got in the car and started the engine. Only got their attention when I started moving