"your friends can assign to you their own nickname for you" is "petnames":
http://skyhunter.com/marcs/petnames/IntroPetNames.html
Quote:
Though no single name can have all three properties, the petname system does indeed embody all three properties.
http://skyhunter.com/marcs/petnames/IntroPetNames.html
Quote:
Though no single name can have all three properties, the petname system does indeed embody all three properties.
Another implementation is in Secure-Scuttlebutt. But those "petnames" are actually gossiped around by default (which I would argue is not very intuitive for people).