Which one “feels” right. As a girl in online gaming spaces ~2006 I got misgendered a lot and it never failed to bother me, because it was wrong. For most of us our gender identity happens to match the psychical body we have, so it’s not usually a problem. For some people it doesn’t, and so it feels wrong to them to be referred to as that gender. (There’s also some people who don’t seem to have any strong gender identity at all, so they generally just go with what society says they are).