Some of the stories alluded to in that article above--like KG saying he was a better tipper, or even Rondo saying saying he carried the team in 2008-- sound like jokes, the kind of thing you say when you're clowning around/trash talking your teammates in practice. Maybe the issue is that Allen was simply too humorless to get along with those guys.
Either way, all of this finger-pointing and tattle-tale telling makes Ray seem childish. Pierce gave him an opportunity to bury the hatchet--Ray could easily have said, "yeah, our personalities clashed, there were some issues behind the scenes that the media didn't know about, but we won a championship" and left it at that. Talking about proposed trades that upset him/made him feel undervalued is fair and reasonable. But airing all this dirty laundry about locker room stuff betrays his reputation for maturity. Even if I were someone who had no emotional investment in his time as a Celtic, I'd find it disappointing and unnecessary.