So name your network to offend them in return. Sheesh.
Not really. First of all, did they intend to target you with their network name? If they did, then I'm sure they would be delighted to discover that they managed to "zing" you. So don't tell them, they're clearly jerks. If they did not target you, you can either ask them politely to change it out of consideration for your delicate feelings, or ignore the whole issue.
So, how does this actually affect you? I am pretty certain that the only time this would even come to your notice is when a WiFi-capable device of yours found it while searching the first time for a network. So after your devices have been set to use your own network this isn't going to be a consideration.
And as to involving law enforcement? Unless the network name is clearly intended to convey a threat to your health or safety there isn't a thing the police could do, in an official capacity, anyway.
And unless your local laws are incredibly invasive there is, as far as I have ever heard, no laws anywhere that control how private citizens name their WiFi networks.