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!"