Here’s something you could only say to a really good friend: “Get behind me, Satan.”
That’s what Peter got hit with after expressing concern for his friend. Jesus had just told the disciples that he was going to suffer and be killed. He also told them that he would rise again, but they couldn’t hear that part. They were too alarmed that he was predicting his own death. I would have been alarmed too.
We are told that Peter took Jesus aside and rebuked him. Peter rebuked Jesus, and not the other way around. Peter had the kind of intimate relationship with Jesus that allowed him to tell him off in order to set him straight. I can imagine Peter saying, “Quit talking like that, Jesus. You need to change your attitude. It’s bad for you and it’s bad for the group.”