A flap jacket is a condom, but not just any condom... You must refer to pussy as flap in order to call a condom a flap jacket.
Flap :: Pussy
Flap Jacket :: Condom
"My roommate was digging through all my drawers, cause he was out of flap jackets"
"Melissa might be a keeper. She doesn't mind football, loves Old Chicago and doesn't make me wear a flap jacket"