The Guardian reports that if you are straight and haven’t used condoms with multiple partners: Donate blood! If you had sex with a sex worker of the opposite sex: Donate blood! If you had sex over a year ago with a partner of the opposite sex who is HIV-positive: Donate your blood! But if you are a man, and you ever had sex with another man? The new rules say you’d better keep your blood to yourself, if you’re in America.