There's a lot.
He held a franchise hostage for nearly a decade by teasing retirement every year and making every offseason a frantic mess to the detriment of his teammates because, even though he looooved playing the actual games, the awfulness of showing up to training camp and doing unpadded throwing drills for a month a year was just too taxing for his $20 million salary. When he retired again, swore it was it, and the team moved on, he changed his mind after they reorganized around his replacement. He then waged a PR war against the franchise, saying they betrayed him, splitting the fanbase, half of whom sided with him. Then he went to play for a rival team.
He crossed the picket line and sided with management when a teammate, who was only getting paid 500k despite having been a top 5 player the previous year, held out for a fair contract. The teammate was shamed into caving and he then blew out his knee in the first game, costing him millions.
He sexually harassed a woman half his age by leaving her voicemails and sending her unsolicited dick pics while his wife was undergoing cancer treatment.
He threw his coach under the bus after the team lost a playoff game due to a season-ending INT by Favre (he would later end three more seasons the same way). The coach was fired.
He made a pariah out of his heir apparent by refusing to welcome, let alone mentor, him.
He campaigned for Thaddeus Cochran.