I've done it... rarely when they are parked, but several times when people have pulled out in front of me right into my lane, I'll give them a nice tap as I ride by. It's mostly for the shock value, as nothing startles a driver more than a loud noise, and the last thing they then expect is a bike to be in their lane going faster than them. Makes a good point too, as it almost always results in either an apology or the shocked "i never considered this as a possibility" face. I'm always careful where I do this though. Never in the rougher parts of town. There you just mind your own business and get on your way.