Back in early 2011, Punk disliked the fact that Miz was getting to main-event WrestleMania against Cena instead of him. Punk's reasoning was that he was the better top heel for the PPV, but management disagreed. Instead, Punk ended up in a losing feud against Orton. This caused alot of backstage heat between the two guys. Punk even went as far as mentioning it on his Best in the World DVD, and claimed management favoring Miz over himself was one of the reasons he cut the pipebomb promo and almost walked out of the company.
To this day, there's still hard feelings (at least on Punk's side), and what we heard them say to each other on Raw this past week wasn't entirely scripted.