The Revenge of the Pyracantha!
See the picture below?
Yep, I planted five of them on the nasty neighbor's side of my front yard. Each plant is said to get 12 feet high and 12 feet wide. Right now, they are only about 5 feet high and a foot and a half wide, so I planted them about four feet apart, just for good measure.
Soon the neighbor guy will be pricked and scratched if he comes too near. Birds will eat the berries and crap on their cars.
Yes, there will soon be a solid wall of privacy. Scratchy, pointy privacy.