It would be quite difficult to form a friendship with a guy who bashed your best friend's skull in. I can just imagine them sitting their having drinks when a new recruit comes up and is likeNegan is just like anyone would be in the post ZA.... his latent personality traits come out in a consequence free environment. In Negan's case, anti-social and psychopathic traits. Rick would do well to study up on his Andrew Carnegie's "How To Win Friends And Influence People." I don't admire Negan, but I understand where he's likely coming from. He's been VERY reasonable to a fault (which will get him killed eventually...) with Rick who is the real true psychopath in training. Rick really should have just formed an alliance/partnership with Negan after a year or so of paying him tribute. But an antisocial psychopath like Rick doesn't play well with anyone.
Recruit: Wow! You two sure are great pals. How did you meet?
Rick: ...
Negan: ...