Cena is awful as hell. (Yes, I'll acknowledge he's had some very solid matches in the past, is essentially the face of the business, and can at least get a reaction from the crowd).
I mean seriously, that promo was all around terrible. It was hilarious to see how many boo's he got at the end of the segment, contrasted with Del Rio, who in a very small time had almost the entire audience on his side.
I mean c'mon, it's not that Cena is "controversial" or "one hell of an interesting character". The crowd is made up of two groups: those who are smart enough to boo him now, and those who will regret cheering him in a couple of years.