If you mean "facial expression," then possible antonyms include:
* Dismay: A look of distress or disappointment.
* Gloom: A look of sadness or pessimism.
* Fury: A look of intense anger.
* Fear: A look of apprehension or anxiety.
* Apathy: A look of indifference or lack of interest.
If you mean "to support or tolerate," then possible antonyms include:
* Oppose: To resist or be against something.
* Reject: To refuse to accept or allow something.
* Condemn: To criticize strongly or denounce.
* Disapprove: To have a negative opinion of something.
If you mean "to give a favorable reception," then possible antonyms include:
* Disapprove: To have a negative opinion of something.
* Reject: To refuse to accept or allow something.
* Dismiss: To ignore or disregard something.
* Scorn: To treat with contempt.
To choose the most appropriate antonym, you need to consider the context in which the word "countenance" is used.