I bought a box of condums and they gave me a receipt for the condoms. I don't need a receipt for the condoms. I'll just give you the money, and you give me the condoms, end of transaction. We don't need to bring ink and paper into this. I just can't imagine a scenario where I would have to prove that I bought a condom . Some skeptical friend: "Don't even act like I didn't get that condom! I got the documentation right here...oh, wait it's at home...in the file...under "C", for "Condom."