What is the missing number?

When my wife and I decided to get married we'd been going out for a few years. We really loved each other and we wanted everything to be perfect... and pretty much everything was, except that one thing had been bothering me. Her sister was a babe and many times I visited, she would flirt with me, bending over in front of me, things I didn't want to acknowledge.

Well a couple of nights before the wedding, she called me over to help her with some boxes. She was moving out of her apartment. When I arrived, I found her alone on the couch wearing decidedly little. I was shocked and she explained to me that she'd always wanted me and that it was her final opportunity, as these were my last few days as a bachelor. Well, I didn't know what to do. She told me she would go upstairs and wait and if I wanted to, I could follow her, but if I didn't, I could just leave.

I waited for a moment and then went outside only to find her dad almost in tears with joy saying he knew now that I was really the right man and that I had his blessing to marry his daughter. This was a test to see just how loyal I was!

Moral of the story: always leave your condoms in the car.