Malevolent Statistics: calling each other "friend"
Suggested by @mysoulspiralbound !
There's a LOT less of this than I thought! I looked through the transcripts for episodes 1-5 (until John gets his name), and episodes 2-4 are devoid of John and Arthur addressing each other as friend...
Episode 1 has John call Arthur friend 6 times, with 5 clustered in the beginning and one near the middle of the episode. He was still trying to cement himself in Arthur's mind as "I'm friendly, you can trust me, let your guard down," and once they get themselves sorted out, he starts calling him Arthur.
Episode 5 has Arthur call John friend twice. One of the instances is calling out for him, and the other is explaining that he had nothing to address him as in the previous instance.