You use extreme to describe situations and behaviour which are much more severe or unusual than you would expect, especially when you disapprove of them because of this.
You use extreme to describe opinions, beliefs, or political movements which you disapprove of because they are very different from those that most people would accept as reasonable or normal.
You can use extremes to refer to situations or types of behaviour that have opposite qualities to each other, especially when each situation or type of behaviour has such a quality to the greatest degree possible.
If a person goes to extremes or takes something to extremes, they do or say something in a way that people consider to be unacceptable, unreasonable, or foolish.
You use in the extreme after an adjective in order to emphasize what you are saying, especially when you want to indicate that it is something which is undesirable or very surprising.