Ha! Not in our family, we are all horrendously polite and good at sharing equally.
But DHs family are different!
MIL used to serve the veg in hot bowls and handed out hot plates with slices of meat on, and the order to 'tuck in'... which we all did as she would grab her plate, the next bottle of wine or whatever and join us.
.. but she always handed BIL a piled up plate. I always wondered why, there was no obvious reason for it. Then, one day, she handed out the plates and he got a plate with only meat on it, like the rest of us. He poured gravy on it, inhaled it and held his plate op for a refill... before she had even sat down. She gave him her plate of meat, which this time he piled high with veg and tucked in, slurpily (did I mention he east like and Alsation, literally chasing the food down to the plate, even licking the gravy up?). She managed to carve some remaining bits off the already depleted joint onto his dirty plate for herself to eat.
By the time she finished that he had almost emptied the veg bowls and she got very, very little to eat. No one said anything, I wanted to but, given his PFB status, was too scared I'd start WWIII.
When she came to us I sat her next to the roasties, gave her a plate, with slices of meat on, and poured her a glass of wine, before returning to the other plates... BIL was visibly agitated, watching his mum help herself to the best of the veg - and yes, I was childish enough to give him his plate last, well, at the same time as I sat down (again closest to the roasties) 
My prize for that was that MIL would hide a good bottle or two of red behind my chair, putting 'other' bottles on the table. Then she would refill our glasses from the good bottles 