From personal experience, the combination of Corn Nuts and Orange Crush soda. I can't eat either to this day due to that experience. I feel sick even watching someone else eat either.
Thanks to my unfortunate migraine headache accompanied by severe nausea that terrible day, neither can I. It happened when I was a kid, but the repulsion is still just as strong now.
Refurb Dell laptops now come with vomit. http://consumerist.com/2012/01/dell-outlet-sent-me-a-barf-covered-gum-filled-refurb-laptop.html