is there a reason why Milkchick tells Irving to sit in the back and mention a tall glass of water?

I don’t know this just seems so odd to me considering the focus on water in the first season. But I just wonder why he specifically called Irving out and why he decided for him to sit in the back and why also did Irving listen?

Was it a test to see if Irving is still obedient and wants to follow rules and order? was it just meant to make you feel uncomfortable? I honestly don’t know, but I can’t stop thinking about it.