I don’t know why anyone would use the wrong pronouns for another person (As Businesslady says, it all come down to basic politeness and respect.). Businesslady’s point that doing so is unprofessional is also important. When you are hired by an organization, part of your job is to work with the other people your employer has seen fit to hire help your coworkers succeed as much as is reasonably possible. These expectations are part of your job (even though they rarely appear in job descriptions), even if you never work on a project with your coworkers. Making coworkers feel purposely uncomfortable when they haven’t been rude to you is a huge abrogation of this responsibility. You may think a coworker is absolutely crazy, but if a coworker, say, claimed to have been abducted by aliens, and you keep making alien abduction jokes in his presence, you’re a jerk who’s interfering with your coworker’s ability to do his job, no matter what wacky claims your coworker has made. The same applies to misgendering your coworkers.