Popcorn lung is caused by a chemical called diacetyl which is used in butter flavoring for microwave popcorn.
As far as things to stuff in your mouth, plain popcorn's pretty flavorless. It's like bite-sized portions of a rice cake. Only it's made from corn, not rice. The worst snack as a kid besides dirt, was cheese on a rice cake. Which tasted like styrofoam with cheese.
Popcorn is surprisingly good at soaking up a flavor and transporting it to your mouth. Which is why you find so many different versions of popcorn. Caramel, Cheesey, Kettle Corn, etc. In the future, scientists predict popcorn flavored with illegal narcotics. I can't wait for Crack Corn and Methy Pop (lame!).
A long time ago, homemade popcorn was made by dumping oil in a pot along with unpopped popcorn kernels. The most important part of the process was making sure you had a lid, and that you used it. Otherwise popcorn kernels would pop out and cause severe injury. Like surprise.
Somewhere along the line microwaves were invented, and the popcorn industry took notice. They said, "Microwaves are great for popcorn. But how can we get the buttery flavor in there?" and a young upstart in the company suggested, "We could use diacetyl."
"Sounds great! I can't pronounce the word so it must have a catch. What's the catch?" asked the popcorn industry.
"It might be poisonous."
"What's that? I can't hear you over the sound of all this popcorn popping in our factory."
This is how microwave popcorn got it's buttery flavor with its mortal consequences. It wasn't a big deal until factory workers started getting sick, and then a consumer fell ill from microwave popcorn he had twice a day for years. Although he was pretty weird and stuck his face in the bag to inhale the fumes, because he loved the smell so much. That doesn't mean the popcorn industry thinks weirdos should die, but they were disappointed by the news.
"We'll pull diacetyl from all our products." they said.
What can be done with all the leftover diacetyl now that it's not going to be in our popcorn? It can be used as a weapon. Microwave popcorn could be fired at enemies in short bursts. The popping of the popcorn would send enemies into a panic, "I hear gunfire, but I see none! I must be hit!", and subsequent blasts of buttery fumes would infect the enemy.
Do this constantly for a decade and by the end of your military struggle, the enemy will develop a severe case of popcorn lung and will never go to the movies again.