I used to have a friend who thought if two of her friends wanted to be friends, with or without her, they both needed to ask her permission. We had quite the argument over it via Facebook chat. When I refused to ask permission to be friends with another person she was friends with she flipped and accused me of "stealing" her friend I was 45 years old at the time( She was in her late 20's , maybe early30's) , reminded her of that and told her I don't need anyone's permission to pursue a friendship, she then tried to shoot down the friendship from the other end by telling the other person, that I would not ask permission - Other person laughed at her too. She claims "all her friends ask her permission to be friends with each other, otherwise they are not her friends".
She has not spoken to either of us since, and has told several folks in our mutual group that I will "steal" their friends. Personally, I thought this type of thing would be out grown by this time - I guess not.
My long winded point is that some folks will find it rude to pursue a friendship with their friends....but I think it's up to each person to decide for themselves.