shooting blanks into a dead end

When both partners of a relationship have been fixed and can't get pregnant. The male has had a vasectomy and the female her tubes tied or a hysterectomy. The male therefore does not have sperm in his ejaculate and the female no way to deliver an egg to be impregnated.

Female 1: "The sex with Joe was great last night. I love not using a condom."
Female 2: "Hey aren't you guys afraid you'll get pregnant?"
Female1: "We're both fixed. He's shooting blanks into a dead end!"