If you have an idea, say it. In a good group, your idea will be received with the understanding that it's necessarily preliminary and tentative, and you won't have to worry about being punished for it. In a bad group, you'll quickly realize that your major task is to turn your associates into a good group. In a bad group, participants feel little or no commitment to the group's goals. People ignore the rules and get away with it.
Members compete with one another.
Members are offensive, or defensive, or both. Members don't come to meetings, or they attend but withdraw from discussion and don't do any work. You're stuck with all the work and a bunch of ingrates and freeloaders. In defense of bad groups, you should note that few groups start out with this awful set of attitudes and behaviors. They evolve into these patterns because they find that the time spent on group activities is not a rewarding and productive experience.