Brett Favre
There are different types of bad sportsmanship as Favre will prove. After Favre departed Green Bay he spitefully gave the Jets all of the information he could about the organization. It didn’t do much good because he was past his prime and the Gang Green was garbage. Then he began holding teams to ransom without backing it up on the field.

Favre taught Aaron Rodgers lessons about how to manipulate a franchise. He refused to report to summer practice and missed conditioning training with the Vikings. Meanwhile, he bullied them into sending his teammates to Mississippi. Favre lost a lot of respect as he entered the twilight of his career (via Time).