The triangular rear side window in some smaller cars having a hinge on the front edge and a latch on the back edge that opens about 2 inches.
That fart is horrible! Open the fart flaps!
When a female uses a vibrator so powerful it causes the vaginal lips to slap each other causing the lips to make a "fart" sound.
Sarah: hey Jen did you use the penetrator 6000 last night?
Jen: yeah it literally caused me to fart flap it was hilarious.
Sarah: oh Jen you love abit of fart flapping.
When a man gets so old that when he lays on his back his balls cover his ass hole
"Dude I woke up last night laying on my back when I farted so hard my fart flaps landed on my stomach, they are suppose to be snug under my dick"