The idiom bent out of shape is used to describe someone who is very annoyed, upset, or offended — often about something that others might consider a minor issue.
The phrase bent out of shape comes from metalworking or car repair. When a piece of metal, like a car's fender, is bent out of shape, it's been deformed so that it no longer has the correct, functional shape. It has to be straightened out. When applied to people, it suggests that a person's normal, calm demeanor has been twisted by anger or stress. Something has caused them to act in a way that isn't normal for them.