It is actually a pretty common scam. I worked at DQ for a bit and once in a while we'd get someone with the same story about how their allergic to tomatoes but got them anyway and then for some reason ate them anyway lol. My store was small and it was quite easy to keep track of who bought what, we didn't even sell lots of burgers so we could tell they were lying.  However people DO have allergies. The scam works because allergies exist, and definitely allergies to onions. EPI pens exist for a reason. What I don't get it why the morons didn't check to see if Dominos made a mistake and put them on their by accident before the kid ate it. Idiots all around.