If you promise to be somewhere and then fail to show up, people may think of you as unreliable, or get angry with you. If they get angry enough, they might ostracize you. To “ostracize” means to cast out of a group, or exclude from a community.

Example: “Feelings about the recent political elections were so strong that I was afraid my friends would ostracize me if they found out that I had voted for the other party.”