Just because you may be slightly annoyed by the start of someone's sentence doesn't mean that you can completely disrespect and invalidate them. It takes a lot of courage to come out to anyone about their sexuality or gender identity. So, for the fact that you would do something like that to someone makes you a terrible person. You may not agree with them, but the least you could is respect their pronouns. You constantly call cis gender people by their proper pronouns, so it shouldn't be hard for you to do it for a person identifying as non binary of transgender.