British author Roz Kaveney discusses Why trans is in but tranny is out - the language of transgender. Money quote:
Right now, trans is just about universally acceptable - though in recent years there was a fight over whether it should be an adjective or a prefix. A trans woman, the argument goes, is a woman who happens to be trans as she might be, say, blonde, but a transman is some special and distinct order of being.
For a while, it seemed as if some younger trans men were going to successfully reclaim 'tranny', at least as a 'smile when you say that' epithet, or a 'we can say that about ourselves; you can't' in-group word like 'queer'. It didn't take, though, partly because it had never stopped being used by would-be hip lad journalists to abuse not only actual trans people, but a list of 'weird' people seen as non-gender-conforming.