In-laws toy with woman's food allergy in horrifying letter to agony aunt

My In-Laws Are Careless About My Deadly Food Allergy is a letter sent in to The Cut's Ask Polly column. It's the second-most amazing agony aunt letter I've ever read.

I have a very severe allergy to mushrooms ... Since then, most meals we have shared at my in-laws' house have had very limited options for me. Somehow, they manage to find a way to add mushrooms to almost everything. One time, they made a point to make a special plate of mushrooms and pass it around. My mother-in-law said, very rudely, "I would've liked to add mushrooms directly to the salad, but SOMEBODY has problems with it!" They even added mushroom powder to the mashed potatoes at one holiday dinner. My mother-in-law claimed it was a new recipe she'd found.

This is just the beginning; it'a rollercoaster ride into mycological madness.

Following is my number 1, posted by Slate's Dear Prudence in 2012. First, the shot...

My mother-in-law hates me ... the problem is that after each visit, I wind up with a bad case of diarrhea; my husband does not. I don't know if the other in-laws are affected, because if I asked, it would get back to her. I suspect that my mother-in-law is putting something in my food or drink.

Then the chaser.

You had suggested swapping plates with my husband to see if my mother-in-law would react. However, as you noted, that would have required bringing my husband into my confidence. I did not feel it was wise to do that, because he already didn't believe that his mother treated me badly. But the next function was at Easter. She provided a traditional prime rib dinner, set up buffet style, and I could see no way that could be problematic. However, when we arrived at her home, the dinner table was set with place cards and in front of each was a ramekin of horseradish sauce and a small pitcher of au jus. When nobody was looking, I switched the ramekin and pitcher between my husband's place and mine. After my husband and I returned home, he became wracked with diarrhea, but I was not ill at all. In the morning I told him that I had switched the horseradish and au jus. He looked at me with such hatred in his eyes that I knew he had known all along what his mother was up to.