Let's explain.
Favre, who long had a great relationship with head coaches in Green Bay, was rarely called on the carpet with the Packers, especially in front of the team. With the Jets, however, the sources say that Favre has been called to what they dub "the principal's office" and grilled about making bad throws that turned into interceptions. Those same sources say this is not just done in private. Mangini will also grill Favre about his throws in front of the team, just like everybody else.
For a guy who for all intents and purposes earned the right to be treated like a king in Green Bay and treated with a certain respect not bestowed upon others, this approach must be quite the awkward awakening. In Green Bay, Favre had his own locker room area to dress, an office area among other perks. He certainly wasn't called out.
In addition, there have been grumblings about how often the Jets have to meet. Many players privately take issue with how many meetings they have under Mangini.
But the kicker that wears on Favre and others are little impromptu quizzes that Mangini often hits his players with during the week. Mangini will call guys out and ask them personnel questions about their opponents. Usually that's OK, but the difference here is that Mangini will ask offensive players who opposing offensive players are and if guys, including Favre, do not have the correct answer those players also get called out in front of the team.
Again, nobody ever knows what Favre will do, even after he announces his intentions. However, everyone close to the situation feels he will, in fact, walk away and walk this time for good.