The first time I can remember being sick was as a wee child, maybe two years old, after eating a lunch replete with green bell peppers. The subsequent vomiting made such an impression on me that I spent the next 30 years unable to eat them. I wouldn't even eat a pizza with peppers on half of it (or picked off) because the smell alone would send me gagging.
I finally got over it and will now consume them cooked. (Raw is still inedible.)
What is the one food you hate so severely that the mere sight/smell/mention of it makes you cringe?