"I'm Reformed!"

"Sirius Black!" scolded Professor McGonagall. He skidded to a halt. 

"Yes, Professor?" He asked with his infamous grin. 

"No running in the hallways! How many times must I tell you this?!" 

"I completely understand, Professor and it will never happen again," he said apologetically. Professor McGonagall gave him an unbelieving look. 

"It's true! I'm reformed! I've seen the error of my ways, and -- Oops! Got to go! See you later, Minnie!" He yelled over his shoulder, sprinting the opposite way down the hallway. A minute later, three Slytherins rushed past Minerva, and they were covered in pink goop. 

Professor McGonagall was trying hard to hide her amused smile as she shook her head disapprovingly. Sirius Black never changes.