Which institutional sustenance do you imagine to be more foul, prison or school cafeteria food? Both are legendary for being less than appetizing. Even media portrayals of the servers of these meals are unflattering; I suppose it's the idea of "shooting the messenger."
Take a look at these meals and make a guess as to whether you'd see it more easily fitting on a drab, graffiti-scratched school table or a drab, bolted-to-the-floor prison table. Then see the remaining photos and check your answers here.
Images: cavemancircus.com
Aramark comes to mind.