A pharmacist may refuse to accept or fill a prescription under all of the following circumstances EXCEPT when:

A pharmacist has the professional responsibility to ensure that prescriptions are valid and safe for patients. However, some situations allow pharmacists to refuse to fill a prescription, while others do not.

In the specific case of a patient being known to be HIV positive, this does not constitute a valid reason for refusing to fill a prescription. Pharmacists should not discriminate against patients based on their health conditions, including HIV status. It is important to respect the privacy and rights of individuals with HIV/AIDS, as this condition does not inherently affect the legitimacy of a prescription.

On the other hand, there are valid reasons for refusing to fill a prescription when a patient is known to abuse drugs, if the prescription is not properly written (such as in conditions where it should be in ink), or if a medication is expired. These reflect concerns regarding the safety, legality, and effectiveness of the medications being dispensed. Therefore, the correct answer indicates that being HIV positive should not be a basis for refusal.