Reportable?

Not ganking isn't usually malicious, they just decided their time is better spent elsewhere.

AFK farming might just mean they feel they are weak and won't be able to help yet.

Now when they admit that their actions are malicious, then of course you should absolutely report them and they can be punished for their behavior. They don't have to admit to trolling for you to report it, but keep in mind that a disagreement with the jungler doesn't automatically mean they are trying to screw you over.