Nal was a bully of yours. You never really knew why, but it still doesn't change the fact that he is

But you have been hiding your eyes. You have Heterochromia/Central Heterochromia, but you cover them up with contacts

You were getting books from your locker, when Nal came and slammed his hand above your head, and when you turned around, your eye twitched slightly, causing a contact to fall out

He looks at you for a second, and then notices the change in eye colour, staring