Patient: blah, blah, blah, some unreasonable request.
Me: We will be happy to help you, but right now you have already had all the pain medication I can give you right now. If you will return to your room, we will be able to talk further when I get there.
Basically, I tell them that PRN doesn't mean scheduled and just because it's been two hours, that doesn't mean that you will get that medication every two hours....especially if I notice you sleeping/passed out. If the patient becomes unreasonable/loud/abusive, i tell them that their behavior is not helping their situation and that this outburst of energy shows me that you are feeling better and not in need of more medication.