Let's get a few things straight.
1) Not accepting a flag is not backstabbing. If I don't think your flag will benefit me, or if you simply flag for a position and not to me directly, I may not accept it.
2) If I flag to you and then you subsequently attack me in what I consider to be an unacceptable fashion, I may rescind my flag. That is also not backstabbing, it is retaliation.
So, while I NEVER backstab, I may not accept your flag and I may retaliate if you treat me as your bitch after I flag to you.
Deal with it.