The act of releasing anal gas with no underwear on, with such pressure that any residue (poo flakes) left behind on the anus after poo-ing are released into the air.
"I let rip a massive bare bum flaker getting up this morning, you could almost chew the air!"
When you have finished your business on the toilet and find some bastard has left you an empty toilet roll. You then shuffle across the bathroom bare arsed, with your pants around your ankles to get some loo paper from the cupboard.
Her "This morning you didn't replace the toilet paper"
Him "Hee, hee did you have to do the bare bum shuffle?"
Her (furious) "Yes!"
Him (having a hilarious mental picture) "Ha ha ha!!"
Jeff : "Damn, Billy and Sandra don't seem happy with each other!"
Mike : "No shit, they just got back from the cinema, I think they're having a Barbument..."