And in direct response to that comic (demisexual isn't even a gender, smh...), here is a neat post about the history of demisexuality and how that term came about, largely through discussion on the AVEN (Asexual Visibility and Education Network) forums. Not, you will note, on roleplay forums.
http://pianycist.wordpress.com/2013/05/08/the-development-of-gray-asexuality-and-demisexuality-as-identity-terms/
And to be honest, the "it's not a real word" argument has never really held water for me. It's a perfectly respectable mashup of a common prefix with a defined root word. Where are words supposed to come from, exactly, if not through means like the above described? Maybe from a word tree in the deep exotic Amazon where linguists must go on pilgrimage to harvest only the ripest fruits which they slice open with a ceremonial knife and then listen to very carefully for a little whisper of the new word from the squashy insides of the giant fruit? I know compared to other languages English is bonkers, but it's not quite THAT bonkers.
You don't have to subscribe to the same label or whatever, just recognize that some people find it a really useful term to use to identify what they're feeling AND to find a community of similar people. Again, a lot of asexual or, really, anything-but-the-hypersexuality-sold-to-us-in-the-media folk find it very comforting to know they aren't broken, defective, or even alone in having feelings like this. It is a very useful term to them. And that's something that's pretty easy to respect - after all, they get to decide what's important to themselves, right?
All it takes is accepting that maybe something is more important to them than it is to you, and being cool with the idea that they know more about their sexual orientation than you do. Or, more generally, as the gospel from the great sages says... 'Be excellent to one another.' /sweet guitar riff