I determined that he didn't like rap probably because of the subject matter. That's why most people who don't like rap don't like rap.
I find that people that dislike rap do so for a variety of reasons.
It is without doubt sometimes the lyrics.
Sometimes it's the attitude.
Sometimes it's because the one disliking it doesn't regard it as "proper" or "real" music, citing the absence of melodies, instruments, singing allied to the stealing/sampling of known hits of the past etc.
Sometimes, it's the older generation of Black people not liking their younger generation seemingly flying in the face of what they feel they've had to endure to get somewhere after centuries of "difficulties."
Sometimes it's because some White people feel threatened by either Black or Black inspired rebels flinging their notions of respectability and "fairness" in their faces and not remaining polite or harmless.
Sometimes it's because they just dislike the overall sound of the genre.
Sometimes it's because people dislike the influence it carries over their young........
And so on.
I know, not all rap is about bitches, hos, guns, weed, and self-hype
Neither is all rock. But almost exactly the same arguments have been put forth against rock music since the 1960s.
Funny thing is that the subject matter and the way certain people, especially women, are viewed is more or less identical across both genres. There's less gun glory in rock, true {unless you happen to be Ted Nugent}, but rap's gun consciousness seems to me to be absolutely in step with America in general and the notion of the right of the ordinary citizen to bear arms.