I've made use of the distinction between a pain being bad and a pain being bad for someone --this can be taken as roughly tracking either the subjective/objective value distinction or the agent-relative/agent-neutral distinction. While there are a lot of issues that this raises (organic unities, harmless bads, Temkin's 'Slogan', Parfit's Mere Addition Paradox, etc), I want to comment on whether a pain can be bad without being bad for anyone as the arguments below claim.
As I've implied, I think ultimately its not possible to have a pain that is bad but not bad for anyone, but there are examples which should give one pause. I've mentioned fetal pain, here's a few others:
Philosophers love the fact that people given lobotomies and leucotomies for chronic pain tend to report that the pain is still present but that it doesn't bother them. We get similar reports with various opiates and strong sedatives.
People adept at meditation and hypnotic analgesia sometimes report that they are disassociated from their pain while in these states --I seem to remember that the Buddha somewhere advises that when one gives up attachment to her pain, the pain does not go away but she no longer suffers from it.
Finally, I've at times been tempted to argue --for various technical reasons having to do with the way I think pains get their objective and subjective badness-- that certain deserved pains are neither bad nor bad for their sufferer. That is, Hitler's pain wasn't bad for Hitler --when he stubbed his toe, nothing bad for him occurred. If such a conclusion held, then it would seem plausible that there could be pains which were themselves bad but not bad for anyone.
These are, I think, prima facie plausible cases of a pain being bad but not bad for someone (in fact, if we add certain Moorean intuitions about the nature of intrinsic badness --esp., the isolation test-- they can be made even more plausible).
Myself, I think that this plausibility turns on several mistakes about what pains are (notably, identifying pain with its sensory component alone) and some related mistakes about the nature of value. Thus I do not believe that there are pains that are themselves bad but not bad for someone.
But this conclusion is harder to come by than it at first may seem.