I was a server in a nice Northern Italian restaurant. I brought a plate of polenta to a table that was garnished with sautéed porcini mushrooms. The mushrooms had just arrived, shipped from Northern Italy to us. When I removed the "lid" from the plate, the mushrooms all had little worms squirming out of them. Luckily, as I was removing the lid I was describing the dish and the guests were looking at me and not the food. I quickly put the lid back on and said, "this is improperly garnished, I'll be right back". They quickly fired another (without those imported worm-shrooms) and all was well.
Close call though. Really gross considering a number of others had already ordered it.