I know I first saw the reference here from Rum and it made me laugh because a group I know has used that euphemism for a while. The root of it goes to a running gag on the tv show How I Met Your Mother. The main character does not want to relay to his kids what they were actually doing so whenever it comes up in the story they're having a sandwich, usually a hoagie... e.g. the hilarious Jason Segal as Marshall in a flashback to their college days...
