second update of the day for this story.
In 1976, Sirius Black was a fifteen year-old boy who was ruled by his hormones, emotions, and anger. Parallel to his inflated opinion of himself, Sirius had an increased determination to avoid humiliation at all costs.
The boy had a twisted sense of justice; he wronged those who wronged him. It did not matter to him why Myrtle would refuse him. He did not consider why she did. The only thing on his mind was getting even. It made sense to him—she humiliated him so he had to humiliate her.
When a few sixth year Gryffindors taunted him during lunch for being rejected by 'geeky Myrtle,' he put his plan into action.
"Well, mates," Sirius had said, lowering his voice as if to impart a secret. "I dodged a bullet there, actually. Turns out, quiet and innocent Myrtle has slept with half the guys on the Ravenclaw Quidditch team." he noted that the older Gryffindors believed him. "It seems Moaning Myrtle isn't so quiet and innocent after all."
The rumor mutated from there. By dinner, it had spread throughout the school that Moaning Myrtle would drop to her knees for any guy. By dinner, Sirius' humiliation had been forgotten.