I know this is a dumb question but........

Not only does Jason like to torture people for fun, but he has deep resentment towards Rize from an incident that happened years ago. It's a long story, but if you read the manga, it'll answer your question.

Jason is a sadist that enjoys inflicting pain on people, without exception. It's nothing personal, he just finds him fun to hit.

Jason doesn't hate Kaneki at all. The reason for Jason to torture Kaneki is because he wanted to do it to someone else. You probably don't know but the name "Jason" is just the name he made for himself after he gained another personality since a while ago he was tortured himself in the same way by a CCG investigator. After that, he gained another personality, killed the investigator that tortured him and roamed the streets as "Jason". As far as I know his last name is Yamori but his first name is not "Jason". In Root A his son explains that.