The act of placing one's posterior against that of another and farting, thus safely depositing the fart in the recipient for later retrieval.
Deav asked his brother at the Indians game, "If you fart into someone's butt, what would you call that?" A guy in the row behind responded, "Well I'd call it a safety deposit box."
Deaver: "I gotta fart!"
Neil: "Quick, stand up and use the safety deposit box!"
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.