"Listen, it's not that big of a deal, okay?"
She rolls her eyes at you, "Not that big of a deal? Are you saying you want to fuck me in the ass? Or ... do you want me to fuck you in the ass?"
You wave your hands frantically. "No! No. Just no. Look, what I mean is, after we graduate, you can get your pussy back. When you think about it, it's not that long of a wait. Besides, look at the positives. First of all, standing to pee? Pretty nice. You can do it anywhere, too."
"Gross."
"Alright, alright," you say, realizing that it's not going to be easy to calm her down about this whole situation. You've have your penis your whole life, so it's hard to imagine what could be better about a penis versus a vagina. "How about this, if you end up with a big one, you'll be the coolest girl in the locker room, right?"
That got a laugh out of her. "Yeah, and I could really rub it in the face of that bitch Jen Smith. Like, literally rub it in her face." She kept cackling while pantomiming rubbing her imaginary cock in your face. "How about you suck on that, you cheerleader slut!"
Your girlfriend grabs you by the head and starts humping your face. You try to push her off, but her grip tightens and she fucks your face even harder. Putting a little more strength into it, you finally dislodge the phantom dick from your mouth. She falls to the floor laughing. You'd never really seen this side of her personality before and you weren't sure if it was disturbing or just disturbing you because you could feel your dick chub up a little.
"You know," she says, after she finally falls silent, "maybe you're right. I should be more positive about this. It's only until graduation, I should just try to enjoy it as much as possible. A little dick never hurt anybody, right?" She laughed again, realizing the pun. "But a monster cock could really do some damage!"
It made you feel good that she wasn't so upset anymore, though it was a little worrying. It's one thing to be more positive about it, but you were afraid that this was going to unlock something dark that not even your girlfriend knew was inside of her. She had never been overly shy about sex before, but the way she was acting now, you'd think she was a pent-up sex fiend ready to let loose on the first soul that caught her fancy.