'Discontinues friendship with a user_id or screen_name.
Args:
user_id:
A user_id to unfollow [Optional]
screen_name:
A screen_name to unfollow [Optional]
Returns:
A twitter.User instance representing the discontinued friend.'

def DestroyFriendship(self, user_id=None, screen_name=None):

    url = ('%s/friendships/destroy.json' % self.base_url)
    data = {}
    if user_id:
        data['user_id'] = user_id
    elif screen_name:
        data['screen_name'] = screen_name
    else:
        raise TwitterError({'message': 'Specify    at    least    one    of    user_id    or    screen_name.'})
    resp = self._RequestUrl(url, 'POST', data=data)
    data = self._ParseAndCheckTwitter(resp.content.decode('utf-8'))
    return User.NewFromJsonDict(data)
