Back in elementary school, I found the usuals every so often: coated cardboard (the kind in non-plastic milk containers, but from gravy, most likely), plastic wrap, stuff like that.
Actually having to cook stuff that's like that though, is worse. When I was living in Minneapolis, I worked at an upscale grocery store in the deli department, and for a while towards the end, I was in charge of the raw chicken preparation. This basically entailed sorting the various cut pieces into tubs (after draining the liquid), and then seasoning the whole chickens for the rotisserie. It would come in these 50 lb boxes that I had to haul around, and a lot of the time they were not only cold but frozen, depending on how recently they had come off of the truck. Did I mention that management was always nagging me to go faster? Let's recap.
Frozen chicken + frozen blood/salmonela juice + cheap, thin, crappy food handling gloves + nagging management = thank God I was making $10 an hour at that place. Oy.
Anyway, the bad part came when I was sorting the cut parts. These big meat packing companies are... big. They pack a lot of meat. Consequently, like any big sorting industry, not everything gets completely clean or done up to code. It's just a fact of business. So every now and then, I'd get one of these flukes, because I was handling in excess of 400 lbs of chicken a day, pesonally. Sometimes, I'd get a whole chicken with a neck attached still. Sometimes there were some organs still inside, or nastier, organ matter. Mystery meat, if you will.
What I hated most though, was feathers. Ever take a bite of chicken and get a feather? Tasty, right? Of course not. I mentioned that this was an upscale place, and that's an understatement if you've never seen a store like this. Everything was more expensive. $13 a pound roast beef, 1000 different cheeses, a gourmet chocolate shop, a cooking classroom, a gift shop (need some fine china with that yogurt?), a liquor store (not just an aisle), a restaurant, an chinese carry-out, it just goes on and on. So I'm thinking, if we pride ourselves so much on quality, why does this wing have six feathers on it still? I'd get in trouble for being slow, so eventually I just had to force myself to ignore them, and into the fryer they went. I never bought the chicken there.
Oh, and Somethingawful.com's Comedy Goldmine has this classic, among others.