That Rondo messed up that play, in general was shaky in his floor leadership in this game, and overall has not had his A game, despite some great moments, in this series is likley not in question. It's particularly frustrating for other players if the point guard is off because so much of what is possible depends on him. I don't blame Pierce for having some frustrations, and I think it is a general strength of the Cs that they can have these things out and then move on, which I expect they already have.
However, he who hath not sinned among the Celtics through some pretty poor play in certain games, let him cast the first stone. More frustration may build toward the point guard because guys depend on him, but when big men are failing to rebound such that the point guard and wings are having to bail them out, and when wing players can't hit anything these are failures in the portions of the game the team depends on also. Should the other players be saying to Ray Allen - "Hit a shot Ray, that's what you are paid for!" Is that helpful? If a guy is not trying sure, blast him, it's hard not to blow up at that, and if any guy is not executing in a way a teammate can point out and help correct, absolutely talk to that player.
But quit mid-play on the final shot of the half? Turn away and pout because you did not get the ball when you were suppose to? That happens in many plays, and many times the point gurad realizes and tries to come back to the guard which is what Rondo tried to do and correct his error. Unfortunately, Pierce was staring into the loge seating behind the scorers table when Rondo looked back.
Pierce played a great game and overall has matured in the past few years, so it is not a mortal sin that he had a lapse for a few seconds, but for that moment, he behaved immaturely and poorly and helped make a messed up play even worse. Rondo is responsible for his shaky play and frustrating his teammates; Pierce is culpable in that moment of not behaving like a mature leader.