Just that really. My mil constantly compares my dss (who for all intents and purposes is my son) negatively to his cousins and it drives me MAD. She particularly raves on about my dh's brother's two daughters and my personal view is that she not only favours dh's brother but that she never had a daughter so lives a bit vicariously when she sees them.
My mum doesn't do this with children our side of the family (which is ironic because technically they are step and not bio but you wouldn't know!) but maybe I'm just lucky and mil is a more typical example.
Any ideas/advice much appreciated, I'm beginning to really dislike my mil over this!