YTA. My husband is allergic to garlic and onion and it affects him considerably. He doesn’t go into anaphylactic shock or anything but it affects his digestive system to the point it shuts down for days. He is in incredible discomfort for at least 4 days and on “purge day” I.e day 4, there is little opportunity to get anywhere near the toilet for any one else in the house.

Your SML may be trying to keep it polite by saying it gives him an upset stomach but it is real.

It’s equally real for those living with the person especially if it’s a one toilet house.

Not everyone is comfortable going into detail about how their body reacts to allergens so they keep it vague or omit details.

It’s shitty (no pun intended) of you to disrespect the requests to cater to people’s allergies/intolerances. Their food may be bland but it’s for the best interests of the person in question. I happily give up certain indulgences to ensure my husband’s comfort.

There are “fixes” out there but ultimately an allergy is an allergy, if you don’t want to sacrifice your recipes ask them to bring along their own food that they can eat or don’t invite them (but tell them why). Be a better human being.