One day Severus Snape was in his dungeon grading papers from the potions final earlier that day.
'Hmmm, what do we have here? Potter's paper? F.'
'Miss Granger? B, only because Minerva would hex me if I gave the girl anything less.'
'What do have here? Ehk, Weasley, what is this? A dragon? F-.'
'Next up? Ahh, my star student, Malfoy. Such a wonderful boy, A.'
On this went for a few quiet and scowling minutes, with multiple Gryffindors getting significantly lower scores than the Slytherins. The dungeon was quiet, the only sound being Snape's quill.
Out of nowhere, he heard a distinct commotion directly outside the dungeon door, and naturally, being himself, arose out of his chair with his signature Snape walk to investigate. He floated silently to the door and peered out, hoping to catch the culprit in the act. He was already figuring out how many House points he should deduct, depending on the student.
Malfoy, Crabbe and Goyle ran past, wearing bright pink tutu's complete with pointy fairy hats and little plastic wands, screaming 'I FEEL SO PRETTYYYYY! LALALALALALA! YAYYYY!' before disappearing around the corner.
Snape screamed 'OHHHMAHHGAWDDDD!' and then died.