A pair of boxers that a boy keeps in his room and never washes. These are usually his prized possession in his messy room / closet. They usually smell like the boy's farts, since he would have done so in them many times before.
boy 1: what are these?
boy 2: my fart-boxers, they're always lying around here.
boy 1: oh, nice man; mine are blue.
During a moment of extreme sexual daydreaming or during a masturbationsession, the raging boner manually overrides all bodily functions. Resulting in a non-consented fart.
"I can't make it 5 minutes into that porno without a boner fart, the acting is that good."