lol i cant believe your NEIGHBOUR would do that to your car, i mean jealous f**ks in carparks, yeah, but neighbours? wtf?
my choices would be
A) Confront the mother f**ker and tell him youll key his face.
B) If the storage unit has some sort of flashy door, grab your key and go nuts. if not get some paint and write something smart yet challenging like "Key this bitch", or if his car is outside, write that on his bonnet in some nice engravement, dont be too shy on the pressure though, you wanna go reeeeeaaaal deep
C) Eggs are your friend
D) get one of those really loud horns (fog horn) and sit out the front of his house/apartment/unit where you would think he slept and give him some. only problem with this is you might wanna be quick in your escape as catching you in the act is baaaad.
If i were in your situation, id probably try B) first just to get a reaction. then id park my car somewhere secure that he cant get to