Personal Nicknames

Too often people change their usernames and profile pictures in my friends list and then I completely forget who they are. Similar to nicknames on servers, I wish for the ability to give someone a nickname that only you can see, and will be prioritized over any other usernames and nicknames whether in servers or DM's. It would be just like having a name for someone in a contacts list that is only something you see, while their phone number is their username so to speak.