snoxr500...the simple answer....
BBM is like your text messages, same principal. You can only get rid of folks texting or BBMing you by deleting them from your contacts.
Where you can log out of email, or set them to not come to your mobile........you cannot do the same with your text service and you cannot do it with your BBM service. Both will always come though to your phone. Both are always active.
Ang x