I've always toyed with it, since I was a kid. But the problem is, I have a family and friends, and I'd rather be a legitimate police officer than a vigilante. If my family were to die in a fire caused by a criminal, maybe that'd be enough to push me over the edge and become a vigilante, and if I survived my next meeting with the man, I'd probably just become a police officer anyway.
EDIT: I'd probably put my basic parkour skills to the test, and use distraction methods and knockout techniques to take down enemies without a bullet being fired or a life being taken. I'd probably have a cliche name like NightWind or Blackout, considering I'd wear all black and use the night to my advantage.