Just a short oneshot that came into mind after reading OotP, chapter 17 "Educational Decree Number Twenty-Four".
Enjoy :)
Severus Snape was in his office, reading essays by his students. Potters was of average quality, but the extra at the end was what earned him the grade.
"The reason I failed to do my potion properly was because I was listening to your and Umbridge's conversation. She seemed disappointed that you didn't talk about how I am the worst student you've ever had, and that professor Dumbledore wasn't a raving lunatic who should be put down.
Nice work Prof. S."
As annoying as he was, that Potter sure had style. Sometimes.
The following day Harry was surprised by the big green, sparkly O on his paper.