The key thing is be consistent in what you tell people, and don't undermine people's efforts to cater for you.
DS1 had allergies (facial swelling, eczema, explosive bowels) to milk and eggs and an intolerance to soya so was on a total exclusion diet for about 18m, then weaned up the food ladder until he could eat normally by about 4. It was easier to explain total exclusion than the can have cake, butter, cheese, but not cream, milk ice cream etc.
Through the changes in his diet, I realised that I have what I call a "low tolerance" to dairy. I can eat more processed, fatty forms of dairy in moderate quantities, but milk in less processed forms will have unfortunate consequences for the nearest toilet. In a restaurant I can usually choose something appropriate off the menu. I may have to decline dessert. I don't have to fear cross contamination like people with more serious or sensitive conditions. (DS was inadvertantly "dairied" at a wedding as a toddler by buttered vegetables with somewhat unpleasant consequences for the next week) I haven't sought an official diagnosis, it was hard enough going through the process to get DS seen even though the GP practice had seen the reaction where his face swelled beyond recognition. I've had dietician's advice on his behalf so substitute my diet appropriately. I see no point in wasting NHS time when I can recognise the patterns and self treat anyway.
I do take allergies and similar conditions seriously. I've had to cater for a friend with anphylactic nut allergies whose immune system has phases of struggling with different foods- we realised on one camp that she being made ill by washing up water, washing her plate first helped.
Falsely claiming medical conditions and effectively mocking people you have inconvenienced with them is wrong. We had a brownie (& parent) try to copycat a friend... she wasn't impressed when we rigorously stuck to the health form we were given and she got the dry gluten free bread and restricted choice of cakes etc ("but I can have that at home!"). We can only go on the information we have officially been given which said "no gluten".
It can be grey. Just be honest about it.