Quote from Ross in The One Where Rachel Tells...
Ross: Yeah, I- I'm just, I don't know. I don't understand ... how this happened. We used a condom. Rachel: I know. But you know, condoms only work, like, 97% of the time. Ross: What? What? What?! Well, they should put that on the box! Rachel: They do. Ross: No, they don't! [goes away and retrieves a pack of condoms] Well, they should put it in huge block letters!