I’ve always washed my underwear with my jeans and socks. It’s a standard cold cycle with good detergent, right? I honestly never understood the people who obsess over washing intimates completely separately. But apparently, my mother-in-law is one of those people, and her obsession just destroyed my relationship with her—and maybe my husband—forever.

To give you some context, my mother-in-law, Margaret, has always been difficult. From the moment I started dating her son, Mark, I could tell she viewed me as an interloper. She is a woman who prides herself on maintaining a pristine, picture-perfect life. Her house looks like a museum, her clothes are eternally crisp, and she has incredibly rigid rules about how a household should be run.

When Mark and I got married and bought our own place, I knew I was going to have to set some firm boundaries. I work full-time, I keep our house clean, but I am not going to iron my husband’s socks or spend my weekends scrubbing baseboards with a toothbrush.

Usually, Mark is supportive. He knows his mother is intense, and he usually runs interference when she comes to visit. But last week, Mark was swamped with a massive project at work, which meant I was left to entertain Margaret mostly on my own for a four-day weekend.

The tension was simmering from the moment she walked through the door. She made passive-aggressive comments about the brand of coffee I bought, ran her finger over the top of the refrigerator to check for dust, and casually mentioned that Mark looked “thin and exhausted,” heavily implying that I wasn’t feeding him properly.

I bit my tongue. I smiled, I poured her coffee, and I kept reminding myself that it was only for four days. By Tuesday morning, she was scheduled to leave. I was relieved.

I just needed to get through a few more hours. I decided to get a head start on some household chores while she was packing up her guest room.

I gathered up the laundry from our bedroom and took it down the hall. I was just tossing a normal load of darks into the washing machine. Nothing crazy, just some of my workout clothes, Mark’s jeans, and a handful of my everyday underwear. She happened to walk past the laundry room just as I closed the lid and pressed the start button.

I saw her pause in the doorway. Her eyes darted from the empty laundry basket to the spinning machine, and then she let out this loud, deeply disgusted groan. It wasn’t just a sigh; it was a visceral sound of revulsion. She looked at me like I was something scraped off the bottom of a shoe and told me flat-out that I was doing it “all wrong.” She said that mixing undergarments with “filthy street clothes” was how diseases spread, and that my hygiene was completely unacceptable for a grown woman.

I was taken aback, but I tried to laugh it off to keep the peace. “It’s just a cold cycle, Margaret,” I said lightly. “The soap does its job. It’s how we’ve always done it, and we’re both perfectly healthy.” She didn’t laugh. She didn’t even soften her expression.