We should focus on positive and healthy topics such as friendship building, mutual support and common hobbies in friendship, rather than such vulgar topics.
Well, if not in a vulgar sense, 'jerk off' could be used informally to mean 'fool around' or 'be silly'. So a 'jerk off friend' might be a friend who likes to be a bit goofy or play around in a harmless way.
No, it is completely inappropriate. Such behavior involves sexual and private matters that should not be done in the presence of a friend. It violates social norms and the boundaries of a healthy friendship.
No, it is completely inappropriate. Such behavior violates social ethics and moral boundaries, especially when one is married. It can also cause harm to many people including the spouse and family members.
The most obvious consequence is the destruction of the marriage. The spouse of the married friend will likely be deeply hurt and lose trust in their partner. It can also lead to social ostracism as this is not an acceptable behavior in society.
It is completely abnormal. Such behavior is not only unethical but can also lead to a lot of problems in friendships and relationships. If a friend is doing this, it indicates that they have a warped view of sexual boundaries and respect. It can make the person whose girlfriend is in the story feel violated and can also damage the trust within the friendship.