You look to the fairy, who still has that impossibly smug grin on her face, and frantically neigh, asking her to please change you back. Or rather, you attempt to do that. Because as you neigh, you can't hear human speech reach your ears. Just typical equine neighs and shouts, which of course are unintelligible. You say you just want to be male and human again but what you say makes no sense. Ans apparently the fairy thinks so too because she merely laughs.
"Oh, I am sorry, I don't understand unicorns. Mind repeating, though?"
Angry, you repeat that you would like being human again but it results again in nothing. And the fairy continues to infuriatingly pretend not top understand what you want to say.
"Oops, no, my knowledge in unicorn speech really, really, isn't there. Sorry."
You stomp and snort, trying to stay calm but still reiterating your demands. Demands that are all perfectly reasonable, after all. That fairy has been very unfair to you, just because you called her a firefly. You didn't know she was a fairy! You made a perfectly normal assumption! And it all went downhill from there! You had reasons to be angry and that hasn't changed!
"What's this? You want not to be a unicorn?" says the fairy in mock concern.
You nod vigorously.
"You really want to be human again? Because unicorns are so perfect and pure! You'd be the most beautiful mare ever! You'd be much happier as a unicorn. Can you imagine the number of humans who'd be happy at what I am offering you?"
You neigh in protest. Because you don't care! What you care about is retrieving your body!
"Well," sighs the fairy. "I'll make you human again. You are SO ungrateful though."
Finally! When her dust falls on you, you feel your body changing at once, your bones taking different positions, your ears shrinking, your hooves dividing into the proper number of digits. But... But something feels wrong...
"Oops," says the fairy in a mean voice. "But you DID simply say 'human'. Nothing else."