It's more like if he introduced himself as being a young child or a dog. No-one should be under any obligation to play along with Bob's claims to be an infant or a canine when he is neither.
I would ask, when denying people their self-determination, does it start and end with trans people, or is there more? If someone is raised as a Muslim and converts to Christianity, do you deny them that? Who is the arbiter of who gets to decide who gets self-determination and who doesn't? I doubt billionaires, nor politicians, are the best authority for that.
Also, keep in mind that you're railing against one of the smallest, and most persecuted, minorities on the planet. Why do this? Were you harmed by a trans person in some way, or were you just told to do this by someone on social media? Have you met a trans person and talked to them about their experiences?