Soulja Boy is just lazy rap, its a slow beat with repeating lyrics that has a dance. Not much different than the Macarana, only its made for a different time. I've not heard Timberlake's song, I don't much listen to hip hop because I'm stuck in the "ska is cool, I love ska phase"
Generally, I tell a person if I don't like their taste in music, and if they don't like mine, we don't listen to each others music. There is only a few times that you have to be tolerant of other people's music, in their car, or their home, if they own it. I would imagine your younger brother doesn't own your home, so, I would say no, you don't have to be tolerant. You should put on something that he doesn't like, and then, when he gets all up in you for it, see what your parents do, or tell him "Just be more tolerant"
Then again, I'm sort of a jerk, and I'd do that kind of thing.