I think that it's some combination of a milk round being a boring and repetitive job (for those who have to go between all the universities) and some sort of yo

I think that it's some combination of a milk round being a boring and repetitive job (for those who have to go between all the universities) and some sort of youth/milk imagery. I think it's anachronistic as the only person I have ever heard refer to it in that way is my Dad.