Very true in your case. But I've got to play Devil's Advocate and say that I have also known a lot of people who seem to fake food allergies to get attention or to be in control. Like they'll say they're allergic to one thing, but then you catch them eating that thing at a different time. Or they'll use it a ruse to control what restaurant a group of people will eat at.
I also have to play Devil's Advocate on this, because there's always the possibility that someone will suddenly develop a sensitivity to something that has never bothered them before. It happened to me; when I was young I could eat watermelon with no problems. The last time I ate watermelon, my throat almost swelled shut, so I avoid it. I don't consider it the fault of the person who served it to me; up until that point I didn't know I had a sensitivity to watermelon. It's also possible that someone could have an allergy to something unexpected, e.g. someone with allergies comes into my kitchen, and they have an allergy attack because of my cats' kibble. (I don't know if this is possible; I was just trying to think of something unusual.) If I'm told about someone's allergies ahead of time, I will do my best to accommodate them, but since I'm not used to living with severe allergies I might overlook something, and it's not because I wish to cause someone deliberate harm.