Crust-thumper, noun; a person, typically male, who engages in the sexual act of crust thumping.
Crust-thumping, verb; a sexual act whereby a male engages in vaginal intercourse with a female who is currently menstruating. After the male has ejaculated, he removes his penis from the female's vagina and allows the menstrual blood to dry on his penis, giving a unique rust-like texture. He then proceeds to have anal intercourse with said female. The usual discomfort of anal intercourse, combined with the characteristic texture of a crust-thumper's penis results in almost exclusive pleasure for the male, and a somewhat strained relationship thereafter with the female.
Inquisitive friend: "Hey Ben, where are you off to?"
Ben: "Going to a feminism meeting. They spend so much of their time menstruating all over current affairs that I should be able to thump crust until they're all walking like John Wayne."
No-longer-inquisitive friend: "Aaaaah you old crust-thumper you!"