Scene: High school Freshman, or sophomore English class. Boy sits in class, daydreaming out the window. Teacher calls on him using his first name and due to his daydreaming, he doesn't answer. His daydream of course is about his secret transgender desires. Then the teacher calls on him using "Mister Brown". His brain catches up and manufactures the scene you describe in a vision, complete with him/her in feminine clothing. The snickering is real because the other students know he's been daydreaming. He barely stops himself from saying what his vision did out loud.

You start the tale with him stressing over just how close he came to outing himself. You launch into a flashback of whatever lead up to this scene recounting other times he's been tempted to say something like that. But this is the first time he's come close to doing it. He admits that it's getting worse and there is a real likelihood that he'll actually slip up and do it. Then explore where he goes since it seems he's likely to out himself sooner or later.