https://www.techdirt.com/articles/20141208/13222529362/comca...
It has been proven that in many places at least in the US, it is illegal and in some cases is a felony.
Edit: Further, it is not a good idea to connect to any known SSID unless you know for a fact that it can be trusted:
http://arstechnica.com/security/2014/06/free-wi-fi-from-xfin...
Your neighbor might be hacking you while you think you are legally using their hardware.