My DD is allergic to CMP and eggs, it comes up quite a lot because when we are out there is often not much she can have and I often take along a small lunch box with things in for her.
I have lost count now of the number of people who tell me 'just give her a little bit, its the best thing, she'll get used to it' Errr
.... no.
A classic was 'if you don't let her have the eggs and milk then the allergy will just get worse'. Of course, why didn't I think of that!
My next favourite is 'well, I went to the chinese health food shop and they gave me a list of 44 things I'm intolerant to, so I avoid wheat, shellfish, cheese, peas, pasta and beef etc'
When it turns out they've just been hooked up to some hocus-pocus shit electro-whatsit machine which I think is universally recognised as bullshit. Then they sit and eat a cheese sandwich in front of you saying they are being 'a bit naughty eating this but you'll know how hard it is to just cut things out' 
And of course the ultimate 'well, at least she isn't allergic to peanuts' because naturally no other allergies can be nasty can they?!
I am finding it increasingly hard to just nod and smile at these stupid comments.
Sorry, I know it's a bit of a self indulgent moan of a thread but sometimes it is just very irritating.