I'm going to clean my brother's room without his permission when he is out
Is this a result of something that made you angry?
I gave him a whole year to clean it on his own and its still messy so I feel like kicking his ass.
Its a nice thing to clean up for someone else unless they specifically ask you not to clean their room. If your brother does not want you to be in his room then this may be a bad idea. You could however give him an ultimatum, and let him know that you will clean it if he doesn't within a week or so.
I don't care if he likes it or not, I'm going to clean it.
It's actually nice you want to help him clean, but invading his private space without permission is wrong and out of line. His messiness is understandably frustrating, but in order to prevent problems you need to ask first.