I agree with Kogas on this one. If someone is sending you harassing PMs, you can just delete them unread.
Banning because of PM presents a slippery slope. What if they are sending messages to your email?
Hopefully, when the software is updated, it will include an "ignore this user" function.
In my walk in the martial way, my hope is that as long as I live, I will always be a beginner.