A bitter person sees life through their grudge. When we are bitter we see everything about the teammate we vilify suspiciously. Bitter people make up their mind and therefore only see things that prove how wrong the vilified teammate is and how right they are. They secretly build a case in their mind as they see connections in situations that are actually unrelated but now make perfect sense through the bitter lens. All the vilified person has to do is breathe to offend and therefore further prove that the person is actually our archenemy.