its another word for "bestie bae" except instead of the word bestie you replace it with breast so then it turns into "breastie bae" it can be used casually in coversation in place of bestie
person 1: omg so true breastie bae!
person 2: the fuck did you just call me
sharting is where you fart so hard you shit your fucking pants or in this case you "shart"
person 1: bro i think i sharted
person 2: lemme get a sniff homie