Maybe not cool if the neighbor is sensitive, but totally legal to fly over anyone's property. I keep mine 75-100 feet minimum above just about any property - it's higher than you'd think. Totally fine for me to see what I need without an invasion of privacy, so this enters a zone of ethics - what are you up there for? They don't own the airspace so they can complain all they want. If you can see it from a helicopter or airplane, would they complain? (Obviously need better zoom lens...)