Exactly what it says on the tin.
Off the top of my head:
In the Texas Chainsaw Reboot, the girl who had escaped the Hewitts gets picked up by the group of main protagonists. Her clothes are ragged, and she is covered in blood, and she is to traumatized to really talk about what's going on, she just wants to get the hell away. She starts to relax once she gets in the car, until she realizes they are driving back into Hewitt territory. She starts to freak out, calms down, then lifts her skirt and reaches between her legs..... to reveal a pistol, which she puts in her mouth, and kills herself with.
In Machete, the girl the Federales are trying to rescue claims it's too hot for clothes when rescued. After being carried, naked downstairs, she betrays Machete, stabbing him in the leg with his own... er, machete. As he is lying confused on the floor, she parts her legs, reaches between them, struggles for a bit... before producing a cell phone.
Drug smuggling is more often depicted as mules swallowing balloons of drugs to pass later, but it's not unheard of for the mule to be a girl, and the drugs to be carried in her vagina to their destination.
I know it's got to have happened outside of these three examples, and I'm sure it can be cleaned up, but I couldn't find a trope in existence for this particular situation yet. What I had in mind was less of it's humorous applications, and more of when it's used for shock of the characters as well as the audience.