You've thoroughly enjoyed playing this sexy practical joke on Kristen. She had no idea you weren't her normal panties when she put you on this morning, and now you're so small and so tight around her private parts that it's probably painful for her simply to wear you. You really enjoy it.
Unbeknownst to you, however, Kristen keeps a pair of scissors in her backpack. She doesn't want anyone in class to notice her frantically messing around with her clothes, but she is able to surreptitiously take out the scissors and then place her hand by her side. She slowly slips her hand just under the waist of her skirt and manages to touch you, still digging into her skin.
Two quick snips with the scissors, and you're cut, although you don't feel any pain. Kristen does the same on her other side, and all of a sudden she can pull you out. It takes about a full minute, as Kristen is still moving slowly enough that she hopes no one will notice what she's doing, and you're such a tight fit now that it's not easy. But soon enough she has you crumpled up in her hands.
Kristen holds you like that until the end of class, at which point she rushes to the nearest trash can and throws you in. She wants nothing more to do with you. In fact, although you're not there to see it, she spends the next two hours in the shower, making sure she's washed herself of whatever the hell was going on.
For your part, you're now in the trash can outside the classroom. You don't mind being panties, even cut-up panties, but the whole idea was to be worn or at least in some girl's possession. And if you don't turn back now, you're going to be stuck in the trash wherever it goes.