If the cameras are on their property, they can probably point them anywhere they want. I suggest you smile and waive everytime you go by. Even better, tell your neighbor that you appreciate that he's watching your house for you - keeping you safe from intruders. (Yes, I know that's not really what he's trying to do.) It's likely that 1) the cameras aren't even on, 2) the cameras aren't monitored, or 3) if you act like it doesn't bother you, it will become boring enough for your neighbor to find someone else to irritate.