Go to your "user settings", then "account". At the bottom, you'll see "ignore list". Copy/paste the offensive username into this area. Done. You won't see his posts (except when it's been quoted by someone else) and you won't ever get PMs from that person. If someone really bugs you, best to simply let the admins know who it is and if they get enough complaints about the same person, I'm sure they'll do something more permanent.
Please let us no who it is so we can look into this you can contact Aeros he is the top person for our forum if you want to remain anonymous. Just go to contact us and write what is going on and we will look into this further for you. Sorry for any issues that might be going on and will help you if you would like us to. Thanks