Does a husband's jokingly saying to his wife, "Consider yourself divorced," constitute a divorce, and does the wife's response, "Okay, I will consider that you divorced me," constitute her effecting a divorce upon herself, and is his statement considered an explicit delegation of divorce by which divorce occurs without intention?

It appears that your husband's joking phrase is not an explicit divorce pronouncement, so no divorce takes place as a result, and similarly for your response. Entrusting or giving choice [regarding divorce] without an explicit utterance does not result in divorce unless there is an intention. Your husband should be careful about using divorce pronouncements in jest.