A girl is sharing a room with her sister, the sister frequently brings guys home to fuck and always asks her to buy them some condom. One time she buys a condom in a convenience store where the clerk is one of her classmates, she gets embarrassed, explained her situation, and the guy understands. Then the guy shows her a condom piece and asks her if she wants to know how to use them because she tells him that she doesn't have any experience or something.
That's all I can remember, hope someone finds it!