A code for men. Referring to a heavily used woman; with a stretched and possibly odorous vaginal canal.
Hey bro watch out for Rebecca she is a creaky barn door.
Dude I got laid at the party last night. "Yeah but she's a creaky barn door bro." Ah fuck.
Her legs spread open and you come to the realization that she's a creaky barn door. Shut that door and run like hell.