"Mommy, promise not to get offended if I tell you something?  Promise?" 
Um, okay. 
"You might become famous someday.  You might be famous for having the most food allergies." 

I found it amusing, not offensive.  And I can see how it would look that way to a child who has spent the last 10 years on a food allergy diagnostic roller coaster, especially when one of them is corn.