The question should be more about Pena than Marty. Marty will say what he wants, when he wants to, and he is an equal opportunity criticizer. Don't show him an attitude or get in his face, you'll be sorry.
Did Pena goof off? We know he rarely followed Reds dictates. Do you recall when the Reds made a point of him going to Arizona for winter ball and he refused?
Were there other issues? Before we accuse Marty of being anything more than a perfectionist and someone who likes his butt worshiped, we should analyze if Pena became a prima donna since coming into the major leagues so early with so little basics learned.