*I hate people who do that.
Something can either be eaten or it can't.*
Not strictly true...
I'm not allergic to gluten, lactose or fructose – but I am intolerant to them all.
I CAN eat them, I won't go into anaphylaxis or anything that serious, but I'll feel pretty awful afterwards, and if I eat those things consistently I'll get ongoing, pretty severe symptoms (I was hospitalised this year, before I knew what I was dealing with, for constant nausea, exhaustion, major weight loss and fainting spells).
Having said that, I really wanted something on Christmas Eve that I shouldn't normally eat, so I balanced the desire vs the risk of how I'd feel afterwards and decided to have it.
When your diet's super restricted (and it's not a serious allergy as some PPs are posting about) sometimes you do just think "Fuck it, I want that nice taste for ten minutes once in a blue moon and I'll deal with the consequences later."
Doesn't sound like that's the case with the OP, however...