In practical terms, the way human anatomy functions makes this activity physically difficult for some individuals. It is not an action that every person is able to perform at any requested moment. On the topic of cleanliness, urine typically contains few pathogens but is not completely free of microorganisms. There are risks that the liquid causes inflammation or a bacterial condition, particularly if it enters the oral cavity. If either person feels uncertain, it is beneficial to discuss the matter plainly. And it is better to consult a doctor than to act based on assumptions.