...you felt a weird sensation on your stomach. You lifted up your shirt and found that your belly button had changed into a red button. Your girlfriend had a confused look on her face. You explained "The button creates a button."
"But what does the new button do?" your girlfriend asked
"5% chance it undos the effects of all buttons in some way. Otherwise it usually has an effect only on the thing it's attached to or maybe it's immediate surroundings. I could become an animal, or a Morphic Adaptation Unit, or a MILF, or a-" Your girlfriend reached and pushed your button. Immediately afterwards looking down at the button your girlfriend just pushed you could see the hairs on the hand lifting your shirt vanish as the hand got more slender, and your chest swelled up as it's nipples grew larger and tented your shirt. "Or I could become a girl. I suppose that begs the question if this button changes gender or makes me more girly." You looked at your hair which looked more fine and a little more curly... Then as a test you pushed your button again and your curly hair grew a bit longer, your breasts grew a cup size. "Well I think I'm done pressing that button." You said an octave higher voice.
Your girlfriend however had a mischievous look on her face. Then you realized she was bigger than you, and probably stronger, and she also had the button making button... You were at her mercy now.