(I've been getting a lot of search engine hits from this, and I'd just like to point out that I am not cranky at people who actually have health conditions or allergies! In case it's not clear, I'm cranky at people who lie about it because they think I'll fuck up their diets or something otherwise.)
A customer told me the other day that she was allergic to butter. I wasn't sure how to respond, but I was thinking "you're allergic to saturated fat?" I kept trying to think of how someone could be allergic to butter. So I did a web search. A couple of recipe sites came up with people wanting substitutions because they're "allergic", but most of the sites came up with exactly what I was expecting ....
"Lie and tell the waiter that you're deathly allergic to butter" because you're on a diet or don't like it.
*headdesk* C'mon, people. Just 'fess up and tell us you don't want it! I get more pissed with people tell me they're "allergic" to something ridiculously common than I do when they nicely ask for it be left off. Crying "allergy!!!!!11!" just makes you look like a drama queen. We can tell when someone is genuinely allergic versus when they're just being twats. No, really.