I transgender. You transgender. He, she, it transgenders. They transgender. We transgender.
Hey, how's the transgendering of your car coming along? Yeah, my stepson says that all the cool kids will be transgendering soon. Have you transgendered your dog today?
Does this sound silly to you? If so, consider how silly you sound to me when you talk about "transgendered" people.
It's an adjective, folks--not a verb.