What was the worst dining experience you ever had?

This bad experience might have been while dining out at a restaurant or dining in. You might have been the unwitting victim of this experience or it may have been self-inflicted by your own egregious gastronomic error. The tragic circumstances might involve the location/atmosphere, the company, the service or the food itself. Do tell, please. And if there was a lesson learned or advice you can give to others to preserve them from a similar fate, please elaborate.

I will save my own stories for a little further in the discussion.