Yes the terms do seem to be fluid.
And offend/are non-offensive depending on the person!
{remember all transsexual people are both mentally unstable and contrary to both other transsexual people and cis-gendered people}
I personally loath "Shemale" as it sexualises us and at the same time suggests we are less than female. At the same time, I also call myself a shemale at work....I work in adult entertainment.
Like Bionca "Tranny" does not bother me at all.
Though most transsexual people again loath it because in their opinion
it identify's to them as part of the genera of Cross dressers, Transvestites and 'Hairy panty wearers'
...which of course we actually are!
Many ts's get pissed at me when I call myself a tranny because I've gone a long way with all this from hormones, life, surgery's ....often a lot further than many of them.
The inference being that if I identify as a tranny, then by implication, that makes them Very-tranny!
Which as you will realise is the reason I do it in the first place!