The story is true, heaven help me. It happened about 10 years ago and gave rise to a selection of unflattering statements about and nicknames for my in-laws. DH was every bit as put out as I was. After that year, my level of effort went WAY down.
As always, we hosted, since MIL abdicated her role as family matriarch the second her DH died back when we were still in our 20s. As the only other female, I became the matriarch by default, which meant I "got to" host family holidays. I planned a feast with a military Martha Stewart-like level of precision and perfection.

Every dish was timed to be ready simultaneously, the china and crystal were sparkling, and the house was pristine. DH's family had asked what they could bring. Knowing they always turn that offer into a PITA, I told them I really had it all under control, but they insisted. Here's what happened..........
MIL walked in with a couple of cans of shoepeg corn, put them on the counter and said, "I said I'd bring corn. Can you cook these?" Uh......Geez, when someone "brings a dish," that usually means the dish is ready to eat and not that the ingredients are brought for the hostess to prepare. I was using every single burner I had, so doing anything extra meant throwing my perfect schedule off track. Next, she pulled out a jar of applesauce and bag of red hots and said she thought we'd have candied applesauce. I saw that the applesauce was sugar-free and told her it would taste nasty, hoping that would kill the idea. Nope. She went in my cupboard and found MY applesauce with sugar and plopped it down. I think she started the mixture in the pan, but abandoned it for DH to finish making. She'd also brought roles, but I already had some and I flat out refused to prepare hers.
Then she brought out a store bought angel food cake, saying it's for a family member's birthday, which was about a week away. As if we didn't have about 3 other desserts. She said, "Well, angel food cake is low fat." Then she proceded to pull out powdered sugar, butter and cocoa from a bag and announced that she was making chocolate icing for the cake. I checked out the butter and it was rancid, so I threw it away and gave her some of ours. She got my mixer, started making the icing and that chocolate mess started
FLYING all over my
WHITE kitchen. Did she clean it up? Of course she didn't. She piled icing about 1 inch thick on the cake (low fat no longer

) and chunked the bowl and beaters in the sink, without even running water on them. She walked off and sat on the couch to veg, ignoring the bits of icing all over the counter, cabinets and backsplash. By that time, DH could tell he was about to become an orphan.
I somehow got it all on the table, but I was frazzled. I'd made a homemade cranberry sauce that was to die for. They looked at it without even tasting it and asked, "Do you have any in the can?"

ACK! We made it through the meal, and DH and I went in the kitchen to wash the dishes. Of course, they went to watch TV.

The phone rang and it was a childhood friend calling to let me know that another childhood friend had died (expected) from brain cancer. I looked at DH and told him that was the straw that broke the camel's back and that I was headed to bed. He'd have to finish those dishes and entertain his family. And to bed I went.
After they left, I told DH that if INGREDIENTS ever showed up again, they were
staying ingredients. He had to tell his family to bring it prepared or don't bring it at all. I think that's reasonable. I can laugh about it now, but I was about to blow a gasket that day.