Yes, it is illegal to kill your neighbors, lol. I can see why you may want to though. I have had neighbors like this. I called the landlord. If the landlord refused to do anything, I called the cops and also informed them I tried telling my landlord but he/she wouldn't do anything. Telling them that generally makes sure the landlord pays attention to you in future, because they can get in serious trouble. So that's the way I would handle it. (Be sure if you call cops it is during the time your city or county sets aside as "do not disturb" hours.)