I've had loads of them. Most of them are down to my own stupidity. Numerous times I have eaten or drank too much and ended up vomiting. I also got food poisoning from a badly cooked burger. One story stands out though...
When I was in my late teens, I was temporarily living with my friend and his house was an absolute tip. We had no jobs, no TV and we just spent the entire time stoned out of our domes and laughing inanely. Think Beavis and Butthead and you wouldn't be far off. Anyway, we were really stoned, it was like 4am and we had no food... then we found several pounds of stewing steak in the bottom of his freezer. Unfortunately, we didn't have a microwave. We tried putting the whole thing under the grill, which just browned the outside, but left the inside luke-warm at best.
I still remember standing in the kitchen attempting to eat it in slices of stale bread. We just stood there with blood running down out faces from the raw meat. We were still laughing though.