Ass curtains refers to when an asshole is so worn out from over use as in anal penetration ass curtains develop like roast beef curtains for vaginas.
I backdoor bang my girlfriend so much she has flapping ass curtains.
14π 4π
When a girls vagina is so loose it sags and claps
Jane must have big ass beef curtains
7π 5π
A devious act towards another person to intentionally sabotage them.
My buddy brandon did some behind the curtain ass shit when he gave me his shirt with a shit stain on it before we out in public.