The stinging pain - though slight, almost negligible - is a tether. A burning clearing the taunts from his mind, holding him to reality. (It's not serious, only half an inch in length and so shallow that the blood dries upon contact with the air, yet it's there and it's present and that's enough.) 'Freak' is true enough, reminding him that he is strange, unwanted. Freak he can live with. It's the others that make his skin crawl and eyes mist with the tears he refuses to cry in their presence. He's not lazy, he doesn't spend his time sleeping, doing nothing. (The amount of time he spends in his room is his solitude, his badly-needed escape and room to think, to read and experiment. But they'll never see him like that. They'll never understand him the way that they claim they do.)
It's the inadequacy that's the worst. Always feeling inferior, unwanted, not good enough. (Can't they see how hard he tries, to do better, to be better? Trying and failing and he can't even bring himself to cut deep enough to leave a scar. (Even more inadequate in their eyes should they find never-disappearing marks embossed on his skin.) This way it could easily be an accident, glass broken in a chemistry experiment working all of this pain out of him, spilling his blood the way it deserves to be spilled.)
It's not the boredom that bothers him most. Never has been. It's the writhing inadequacy and worthlessness, always present that drives him to shooting the wall, to loudly complaining and plucking nonsense tunes on his violin. At least it's not blood on white skin. (Of course they don't see it like that.)