The phrase is used as an insult or an interjection expressing disgust or anger. Derived from the Jamaican word bomboclaat, bomboshart is a combination of bomboclaat and shart.
Joe: Hey, where have you been all day?
John: Just finished up in the washroom.
Joe: “BOMBOSHART”
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.