You talk to her

You walk over to her and gesture to her clothes, "Put those back on! What the fuck do you think you're doing!?"

"Uhh, just following the rules. You slow or something?" she says nonchalantly. "Unlock the damn doors and let's get some coffee."

You're stunned but reach for your keys and unlock the car anyway. Once her clothes are in you both start walking, you silently realize this was all a mistake and that she's not immune or resistant to whatever is changing everything. You try to reason with her.

"What about everything we talked about? You were just saying not even an hour ago how absurd this all was, and now you're joining in!" you hiss to her. You try to keep yourself from getting too loud as you're in public. "I thought we agreed on that!"

She shrugs and her tits shrug with her, something you can't help but notice. She's looking around this part of campus while saying, "Yeah but...I mean it's the rules right? Why would I break the law especially when it makes so much sense?"

You sigh, exasperated, as you can't seem to get through to her. Some guy passing by checks your sister's naked body out which triggers you a bit into feeling defensive, but also give you an idea.

You grab her arm to stop you both, turning her to face you, and she goes wide-eyed. "You realize this means any guy on campus can just touch your boobs right? They won't ask you, they don't even have to be nice, they can just grab away."

"No duh, idiot," she says petulantly. You get a little angry as you're just trying to help her now. Your cock is semi-hard and it prevents you from really thinking your next move through.

You thrust your hands onto your sister Amanda's bare tits and squeeze rather hard. She gasps and her eyes widen, face going a deep red, as you stare her in the eyes.

"See what I mean? How does this feel, huh?" you ask as you alternate between roughly kneading her breasts and tweaking her nipples.

She looks away embarrassed but says, "I mean, it's kinda weird, you're my brother. But I know you have needs too...it'd be worse if you couldn't work out some of your frustrations out on me. Just...keep in mind I am your sister after all. I'd prefer if you didn't view me as some sexual object."

You freeze as you realize what she just said, what this all means. Well, you mostly freeze, your hands continue groping your sister almost of their own accord. When you recover you realize what you're doing and stop. Amanda breathes a sigh of relief.

"We...we should get those coffees," you say lamely. The air between you is pretty awkward at this moment. You both start walking again.