yoursecret

You should have face him down right away. Introduce yourself and ask him his name. Tell him you need to back up into the garage. Keep insisting and keep talking. If you can't park then you won't let him wash his car neither. If he gets mad and threaten you or touched you then you got him, call the cops and say he threatened you.

Now that's one possible way to resolve it but if as you say he's a ****ty driver, maybe he doesn't understand your need to back up, then you need to make him understand.

But even before all this happens, have you tried to be friendly with your neighbor, like knock on the door and say hi and get to know him.

yoursecret

You probably did the right thing under the circumstances for all I know. It's easy for me to sit home in front of a computer to second guess people and  I know it's hard to think straight when you're angry. so I wish you good luck and all the best.

yoursecret

It's quite reasonable to approach someone and talk. you wouldn't talk to someone across the street. by the way he's washing his car in the middle of the street, not on his property. even if it's on his property, so what? if he wants to call the cops, all the better.

Approach him and face him down?  To provoke him?  To be the aggressor?  
Keep insisting and keep talking. (to harass him and trespass on his property)