Expelling methane gas from your rectum close to a colored persons face. You can always laugh after with your buddies, but eventually you'll get shot. Because its a hate crime to fart in a black guys face.
They'll usually say something like
"Tha dood yo bustin flow in da niggas face, dissed em' back to the tizzle"
When I was siiting next to that douche, he got really close so I busted flow in his face it was fucking hilarious.
That douche was Bustin flow all day.