when you have explosive diarrhea so bad that it is audible from the next room. It is followed by intense muscle spasms and loud groans and moans from the excretion.
Friend 1: "OMG that girl was busting beans so bad that I felt her pain."
Friend 2: "God I hate that, she must of had some bad veggie food."
It means close to something like a kidding around or to joke around.
It can be said as "bustin beans" also.
after saying you were bustin beans you should say "forget about it" but it is said with an Italian voice....like Mario
friend 1: i ate your mom out last night
friend 2: what the fuck i will kick your ass
friend 1: dude i'm busting beans here! forget about it