"Snape knew more curses than most 7th years"
I can't stop thinking of an eleven year old Severus sitting in the great hall, deep in his books, someone trips over his bench, knocking his quill and spilling ink all over his almost finished assignment, ruining hours of work, only because of this clumsy idiot not being able to watch his steps. I can just see him losing it after weeks of teasing and shouting in a strong northern accent, he just started trying to hide:
"Fucking hell! Look at this shite ! I've been graftin' all bleedin' all day and you've done and knackered it, have ya? Can't even watch where you're bloody going, can ya? Get the fuck outta me sight ! Bloody imbecile"
Everyone falls silent, shocked, not just about the language ,but at the raw fury breaking through the usually composed facade. Four Gryffindors exchanged gleeful looks, their eyes glued on Snape. Sirius grinning,eyes gleaming with mischief, "Calm as a corpse most days, but there's a volcano under that surface.Bet he'll snap again...very soon, let's make sure of it".