When the smell of buttery popcorn is so overwhelming that it seems to attach itself to your nostrils, mouth, and lungs. The smell seems to float around like a gaseous poison. This occurs most often at run down discount movie theaters with poor ventilation.
"Open a window! That stale popcorn is giving me a case of butterlung."
A trip to a grocery store, convenience store, or gas station for the sole purpose of buying an excessive amount of junk food and sugary drinks, usually with friends. A chud run often happens late at night and ends with everyone involved hating themselves afterwards.