My inclination is towards visual examples for I LOVED your example :

C->D--->B

because what you're illustrating is distances from people.

What if there was a bytewise type distance so your could represent things like :

Treat any Friend of A as a friend of mine

{ follows: A: [1, 0] } or { follows: A: [1, undefined] }

I don't care about A's friends

{ follows: A: [1, null] }

I met A, but they're not that close

{ follows: A: [2, 0] }

This would be great for someone I met at a conference .. and aquintance. Specifically I want this so that in user interfaces I can have the oft pined after "filter view by open-ness filter". So on quiet days I can connect with people who are genuinely 1 hop from me, and it doesn't need to include some people who are nice but I'm not yet intimately close to.