Based on when Dumbledore mentions setting his curtains on fire at the end of the fourth movie.
Disclaimer: The characters and canon situations in the following story belong solely to JK Rowling, Scholastic, WB (and whoever decided Dumbledore should set his curtains on fire). I am not making any money from the publishing or writing of this story.
A young, inexperienced, fourteen year old Albus Dumbledore stampeded his way up from the dungeons, trying to reach the safety of the Gryffindor common room from the taunting catcalls coming from the Slytherins behind him. "Albus, Albus!" called his friend Trevor, panting as he tried to keep up with the lanky teenager. He was not the brightest, but was determinedly loyal and particularly useful when it came to dragging Albus out of the many tricky situations he got them both into.
When they reached the common room door, Trevor pulled him straight up to the dormitory they both shared before Albus could scare the new first-years out of their seats. He threw his bag under his bed while Albus paced the room angrily, muttering furiously about their potions professor and his new favourite student.
"Albus," Trevor shook his head at his friend before searching for his potions book to fix his essay. "It's just one essay he beat you on, who gives a flying Hippogriff? Just forget it Albus, at least you didn't get a T like me and have to redo the whole essay. And I have to add an extra three inches. Forget the three inches, I can't even manage the foot he set us in the first place! Oh I hate…" Trevor's ramblings trailed off into Albus'.
"An E, only an E! If only I had included the ninth use of dragon blood, I bet Abrecann wouldn't have known that." Albus stormed angrily around the dorm his boots stomping heavily on the carpeted floor.
"Albus-" Trevor cut in, "He's just a stupid Slytherin, forget about him, he's not worth your time."
Albus paused and suddenly looked up as if realisation had dawned on him. "That's the reason why! Professor Herbert only favours Slytherins! Slimy Slytherin snake. If only I could transfigure them into the snakes they are and put them in that dammed cauldron." Albus was so fuming that if one walked into the dormitory they would assume he had eaten a pepper flavoured Bertie Botts' Every Flavour Jelly Bean had his expression not been so livid.
"Albus it's just one teacher. One out of the how many that like you? You're top in every class, let someone else have the glory for a change."
"Yeah, and it sure won't be you!" joked one of the boys that had just entered the room. He looked at the angry Albus and then raised his eyebrows at Trevor. "I'll let you deal with whatever happened then, no need for us to get involved."
During the small exchange it seemed that Albus was getting angrier and angrier, he had resorted to muttering incantations and flicking his wand. On the other side of the room a lamp smashed, sending small fragments of glass on to the neighbouring bed. In a particularly vicious swipe, the curtains exploded and the flaming fabric swung off the rail and landed heavily on the floor before being doused by various shouts of Aguamenti from the four boys in the dorm.
"Remind me not to get on your bad side Albus," called one of the boys.
"Yeah, we'll leave you clear up the rest, see you," said the other.
Trevor just turned to him with an amused smile and shook his head before continuing with what he was doing previous. Albus simply stared at the pile of smoking fabric at his feet and said, "Oh well. I never really liked them anyway."