I think I find my autistic brother's meltdowns funny
Why do you think your autistic brother's meltdown's are funny?
He has an annoying voice. Don't most people laugh at their siblings when they do stupid things?
You shouldn't laugh at anyone because they are different than you, it's very disrespectful.   You should support your brother, not make fun of him because it can have a negative impact on his mental health as he grows up.  Laugh with your brother, not at him and you will both grow up happier.
He's an annoying fucker.
I'm sure your brother can be annoying sometimes, but it can be hard to be autistic. He will probably do better in the long run, and thus annoy you less, if you support him when he's melting down instead of laughing.