"Missing Condoms" joke

A young couple with a box of condoms proceeded to do the wild
thing. When they were finished, she discovered that there were
only six condoms remaining in the box of 12, so she asked him,
"What happened to the other five condoms?"
His nervous reply was, "Er, I masturbated with them."
Later, she then approached her male confidant friend, told him
the story, and then asked him, "Have you ever done that?"
"Yeah, once or twice," he told her.
"You mean you've actually masturbated with a condom before?" she
asked.
"Oh," he said, "I thought you were asking if I'd ever lied to my
girlfriend."