How to tell roomate "YOUR DOG STINKS"?

If your roommate does bathe the dog at least once per month, it should not stink to high heaven. Could it be getting wet frequently or getting into something outdoors that could make it smell awful? If that is not the case and if it is as bad as you suggest, that animal might have some other condition that a vet might need to check out. Some dogs have skin conditions or other medical issues that just make them stinky.