Eye-opener ideas please !

Varah, you got hurt when he said something about your parents right? He would be hurt too if you say something about his. Its a natural reaction.
Try this next time: when he appreciates his mom, go with the flow and appreciate her. When he say anything about your parents (in a negative way), tell him that you would appreciate if you respect them and refrain from talking bad. I am fairly sure this would work, if not, its better to have tried and failed.