If the neighbour had somehow botched/patched my own connection and was obviously taking the ****, I would just go round and sort it.
If its a report coz your ****ed off with them generally, then it's pretty much useless.
Loads of posts have dealt with the rights and wrongs of cable theft, and if it really is a loss of service on your part, and not "bad blood" then sure report
Otherwise, is it really worth the hassle just to 1UP an annoying neighbour, I know for a fact where I am, its really not worth it!