When a girl is extremely prude and no guy is able to get with her, she is said to have an "Iron Vagina." Hence the name, the vag is impermeable to any male body parts (i.e. dick, fingers, etc.)and acts as if there is a extremely thick sheet of iron covering it, warding off any and all brave, unwanted invaders.
-"Dude, did you get with that hot chick last night, she was so gone"
-"Nah bro, she had such an iron vagina it was un-fucking-believable. i just went home and beat off
When a particular woman exhibits the appearence and properties of major bitchitude, such that pierces the soul to the point which all men fear her. She seems to be the type to not take any shit from anyone and most certainly slaps around any man whom she may copulate with.
My friend's girlfriend is hott but she's a total iron vagina.
Dementors, cruella deville, Sarah Silverman, Fergie, Angelina Jolie, M from 007