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”
A person that is both your best friend and partner. When you have graduated to this level in a relationship calling each other, dude, bro, bud, man is totally acceptable because neither of you are insecure about your love. It’s totally cool.