I'm trying to cut my husbands bff out of out lives slowly so they won't notice.
Why would you want to do that? Has he done anything to make you angry?
My husband's best friend is a total douche and I hate the way he treats me.
Your husband's friend is not very nice to you, but he is not your friend to cut out of both your lives. Let you husband deal with him, tell him about everything he has done. I am sure if he doesn't take action though, it will continue to be rough for you.
I can't because I don't want my marriage to end up like my parents.
It's understandable that you are worried that your relationship with your husband might be damaged if you are blunt about his friends behavior. If he knows you feel mistreated by his friend he may be able to talk to his friend about his treatment of you. Maybe his friend doesn't realize he's being rude.