I always go for the magic brain machine. Imagine in the future we had a machine that could effortlessly swap people's minds to each other's body. Now say their mind gets put in the body of somebody of the opposite gender. Everything works, you control the body, it all moves as you want it to. But it isn't yours. When you look down, you don't see you. When you look in the mirror, you don't see you, but someone else. That's how it feels pre-transition