After rereading A Larger World, something came to mind. When Ethan returned to the Hilltop and stabbed Gregory as a "message", what was the point? Intimidation is what I thought at first but now that we've seen Negan interact with Rick it seemed very out of character for him to randomly try to murder Gregory, the leader of the community that is complying with his demands. Perhaps they weren't meeting their quota but it seemed like they had enough food for them considering they were able to give rick a van full of goods. Another possibility is that he has no respect for Gregory, similar to how he killed spencer. His respect for rick exceeds that of Gregory and maybe that is why he almost killed him. But Negan isn't stupid enough to kill Gregory out of nowhere, as he finds that Gregory is a valuable asset to him because he leads his people under fear of Negan such as when he called off his troops in issue 116.
Just something I was thinking of, I'm gonna chalk it off as a character oversight because kirkman hadn't fully developed Negan in the issues prior to his introduction