Told this story before under different user names.
My sons are now mid to late 20's but before they were born we used to go to my parents and this continued after they were born.
My brother used to stay over with his wife and kids, my brother is hard work, wouldnt get out of bed till gone 11am (even on Christmas Day), this would set my dad on edge and he would be grumpy.
Anyway, one Christmas my middle son was about 3 and was fussing about his dinner, not being naughty but saying he didnt like something and older brother was teasing him. My dad exploded at him, proper shouting at him, my poor 3 year old was sat at the table eating his dinner sobbing.
Me and Ex didnt step in as it would have exploded, my dad was already wound up and shouting so we kept quiet and left as soon as we could. We thought this was the best course of action, say nothing to my dad, comfort my son and leave ASAP.
And from that day on we never left the house for Christmas, always stayed at home, even now the kids have left home i will not leave the house. My parents still host my now long divorced brother (dont blame you in the slightest now ex SIL) and his bad moods still dictate the house. But i dont care as i never get involved and enjoy my Christmas at home.