I took a bite into an apple once when I was about 12, and found half a worm.
Also, more recently, I found a packet of honey-coated peanuts at the very back of the pantry, and they tasted okay, so I ate a whole bunch... only to look down and see a maggot squirm its way out of one. That was not a good day.
Other than those two, nope! I've never eaten anything else truly awful.