Don't bother with revenge.
I felt like getting revenge on the people who threw a brick onto the roof of my mums 2 month old Polo TDI. We all knew exactly who did it. Infact me and my mums boyfriend were going to do a joint revenge attack. The person had a lorry cab parked up in a car park near their house and we were going to throw a couple of bricks through the cab window. We left it a week to see if we'd cool off about the whole situation and we did.
Luckily through means I wont mention we got the insurance to deal with the damage to my mums car. To have the car fixed by VW would have cost £1200, there was no way my mum had that kind of money at the time.
They also caused damage to my mums boyfriends car - My mums old car, the Golf GTI. Don't know if they used two seperate bricks but the back window on the Golf was smashed and the only brick they could find was infront of the Polo. I'm suprised they didn't steal anything out of the Golf.
And to be honest, looking at that scratch, it looks like it's localised. Like someone walking past the car could have had something metal on their trowsers, like part of a belt, and they could have been trying to get between two cars and accidently scratched your car or something similar. I don't know how close the cars park next to each other in that car park or how much room there is after. I'm not saying that's the cause but it's an idea.
Usually if people key someone's car around here or something similar they key all along the one side of the car, if not get out the battery acid or paint stripper. There's been alot of that lately.