Waiters that don't pay attention to "special" orders and think it is no big deal. At lunch on Sunday, I ordered decaf coffee with my meal (such a special order I know ). Well the ditz we had as a waitress didn't think it mattered if I got regular or decaf, and because she didn't want to wait for a pot of decaf to brew brought me regular. Unfortunately, she only admitted this after I called the restaurant to complain because I suffered the after effects of getting caffeine (and that's the only place it could've happened).

Yes, I know that these days everybody is a precious princess and need gluten free, dairy free, GMO free, etc but it is not the wait staffs duty to determine which issues are real and which ones are fake. Either handle the request as asked or let the customer know they can't be accommodated.