Um, hypothetically, if a cat has a younger brother, and he acts bad all the time, is there any way to make him leave me alone?

It's a little upfront work, but it is possible to get an annoying younger kitty sibling to leave you alone. First, anytime he comes near you, growl. Make it a really good, growl, one that says, "Beeeotch! I will CUT you!"

Then at some random time, when he's not really doing anything, jump on him and bite his neck. Not hard enough to break the skin or anything, just enough to make him squeal like a little girl.

And then, when crunchy treats are being handed out, take one or two away from him. This tells him, "I only allow you to be here, and this is ALL mine. You're lucky to get ANY."

Then you may have to growl a few more times, with some fierce spitting, but trust me, do all that enough and you will freak his little asterisk out enough that he'll tiptoe around you and avoid eye contact whenever possible.

This also upsets the people, but whatever. They're people.