The Plaza Restaurant, Mom and kids only trip, Spring Break about 8-10 years ago. In the months leading up to the trip, DS had developed a "sensitivity" to mushrooms that had gotten more pronounced as time went on. We had reached the point that we avoided them entirely. He would get violently nauseaus, and his throat would feel like it was closing up.
It's a nice evening in MK. We alert the staff that he is allergic to mushrooms. He orders the cheesesteak plain. They bring our meals. Three or four bites in (they were quick bites - he was a preteen boy - you get the picture), he says his lips are starting to tingle. Stops eating. Says he doesn't feel well, and he's feeling like breathing is difficult. There's no way I'm messing around with anaphelactic shock at a theme park. So we alert the staff, and they call the paramedics. Yep, the MK paramedics.
Much to the eternal embarrassment of DS and DD, two emergency responders and a gurney the size of a small boat come rushing into The Plaza. A couple of quick checks, and they say he won't drop dead within the next couple minutes. But they suggest we head to the infirmary. So off we go, DS under the power of his own feet. (NO WAY he was getting on that gurney! Not unless he was unconscious!) The nurses give him an antihistamine and a barf bucket. We spend two hours in the "MK ED." They were very nice, and I GREATLY appreciated their care.
But it wasn't exactly how we were planning on spending our evening!
So, yeh, our most memorable meal ever at WDW. The OP did say for any reason!
When we got home, I took him to an allergist. Who determined that it is not a true allergy, that eating mushrooms will never actually kill my son. Will make him miserable for many hours, cause him to barf violently, and to feel like he can't breathe - but won't kill him. Some of the best news I ever got from a medical professional.
For the record, we have also had many, many, many great meals at WDW. And dozens where the restaurant/kitchen staff did a great job of dealing with his mushroom sensitivity. So please don't read this as a "Disney doesn't do a good job with food allergies" post. They do excellently. But as anyone with food allergies/sensitivities knows, no one's kitchen but your own is perfect. And sometimes not even your own.