LOL! - I'm with you on this one, Heather, and I don't buy the rationalizations either that some of the other posters here have put forward to justify this type of behavior.
What they seem to conveniently forget is that when they snap such pictures in store fitting rooms, they are doing so on private property (in this case, the retailer's or mall owner's premises) and can be deemed to be trespassing and violating others' privacy by doing so. It is the same principle that is followed by certain churches, museums, and business establishments that forbid photos to be taken on their property for a variety of reasons, all of which are perfectly legal and justifiable within the context of how they wish to interact with the general public.
Too bad that these narcissists can't just be honest and admit that they do this to get their jollies for fetishistic reasons, as opposed to simply dressing in women's clothing as an expression of their gender identity like the vast majority of us. This falls into the same category as having sex in public places because the possibility of being caught in the act is a huge turn-on for some people, and just heightens the thrill and the eroticism factor associated with that.
And where they really lose me is when it comes to taking photos of themselves wearing articles of women's clothing that they actually have no intention of buying. If they are not purchasing the item in question (or perhaps planning to buy it later upon further reflection), why does it matter if they look good, bad, or indifferent in it except maybe within the context of a "been there, done that, scratch it off my Bucket List" scenario and providing visual proof of that personal accomplishment.
My attitude generally is whatever turns your crank as long as children and animals aren't involved, and I'm not judging. But on the other hand, I also don't have sh*t for brains and my B.S. detector works just fine - thank you very much.
What does concern me, though, is that this is the kind of stuff that reflects badly on the TG community as a whole, and just serves to reinforce the creepy and fetishistic stereotype that the "haters" like to hang on us.