Ewwwwww. I'd heard of the Holy Grail, but that... The following is from Wikipedia.
"The first reference to the survival of Christ's severed foreskin comes in the second chapter of the apocryphal Arabic Infancy Gospel which contains the following story:
And when the time of his circumcision was come, namely, the eighth day, on which the law commanded the child to be circumcised, they circumcised him in a cave.
And the old Hebrew woman took the foreskin (others say she took the navel-string), and preserved it in an alabaster-box of old oil of spikenard.
And she had a son who was a druggist, to whom she said, "Take heed thou sell not this alabaster box of spikenard-ointment, although thou shouldst be offered three hundred pence for it.
Now this is that alabaster-box which Mary the sinner procured, and poured forth the ointment out of it upon the head and feet of our Lord Jesus Christ, and wiped it off with the hairs of her head."
To me, this just screams fake. Luke 2 tells about Jesus' circumcision, and no mention of a cave - inn or stable, maybe, but not a cave.
Luke 2:20 - 21 And the shepherds returned, glorifying and praising God for all the things that they had heard and seen, as it was told unto them. And when eight days were accomplished for the circumcising of the child, his name was called Jesus, which was so named of the angel before he was conceived in the womb.
The article goes on to state "Foreskin relics began appearing in Europe during the Middle Ages" and "Depending on what you read, there were eight, twelve, fourteen, or even 18 different holy foreskins in various European towns during the Middle Ages."
Fake, fake, fake! First, why would anyone in his/her right mind preserve foreskin from a circumcision? Let alone keep it in the same box as the storage container for perfume? Second, these relics mysteriously start circulating centuries after Christ's death? Very strange they weren't known about previously, if genuine. Third, there are eventually 18 of these circulating around? At least 17 were fakes for certain. This comes across to me as a very fake claim, not to mention gross. And I think, greatly irreverent, considering it is said to come from God Himself, not just a mere man.