I proposed a way of doing this called Relationship Status, which not only allows you privately petname pubkeys also categorize your friends and assign scores to them in a true Web of Trust fashion. Clients can do all that in a public or private way with the same event format.  

https://github.com/vitorpamplona/nips/blob/relationship-status/81.md 

 How do I upvote this. 

 This is suitable, and accomodates testimonials as well via summary when public