You've just joined a pick up group and zoned into your favorite instance. The group's warrior rushes in wielding an ice barbed spear, and when asked why they aren't using a shield, replies "I'm not that kind of warrior!" At that point, you just have a feeling that things are going to go downhill from there. As time has passed, I've sort of developed a mental list of warning signs, and a warrior who doesn't own a shield is only one of many, many things on my list. However, what are your own warning signs that a group is about to go bad?