The look of sheer horror and disgust in the faces of waiting staff when you use the word 'disease'.
Why call your condition an "intolerance" or "allergy", when the word "disease" makes a much better impression and helps put you more at ease on the already terrifying experience of dining out.
For added effect, I've started to ring a bell as I enter a restaurant to signify that I have Coeliac Disease - and I say the D-word in my most stentorian voice.
Links: