My car got keyed how should I respond, if at all?

[B Dids]

Keying somebody's care is not a proper response to this however.

That said, I'm not sure what you can do. You don't know who did it, so short of just blowing up your car in such a way as to revenge at the most people, it seems like your only possible response is to be annoyed, move on, and park less like an ass.