I've seen this happen too and despite the apprehension of causing a "fuss" the only proper response is to fight back through proper channels and use the laws in

I've seen this happen too and despite the apprehension of causing a "fuss" the only proper response is to fight back through proper channels and use the laws in place designed to protect you and potential future victims - in the UK there is harassment law, the malicious communications act and court injunctions you can take out. The police tend to take quite a hard line too so don't suffer in silence.