Easy one? Last time I saw one of these I was a student... They're nice and rare... but GREAT to look at!
(Yech! - Andy)
It's a teratoma!
Great definition from Wikipedia..
A teratoma is a type of neoplasm (specifically, a tumor). The word teratoma comes from Greek and means roughly "monstrous tumor". Definitive diagnosis of a teratoma is based on its histology: a teratoma is a tumor with tissue or organ components resembling normal derivatives of all three germ layers. Rarely, not all three germ layers are identifiable. The tissues of a teratoma, although normal in themselves, may be quite different from surrounding tissues, and may be highly inappropriate, even grotesque (hence the monstrous): teratomas have been reported to contain hair, teeth, bone and very rarely more complex organs such as eyeball, torso, and hand. Usually, however, a teratoma will contain no organs but rather one or more tissues normally found in organs such as the brain, thyroid, liver, and lung.
Next time you feel a lump in your groin (and it's helluva painful) - it's more likely to be a ovarian torsion or appendicitis than a teratoma. Don't fret! Teeth and hair are probably NOT growing inside your groin (for men - the pain would occur in your testes - and then NO, it's not appendicitis).
CONGRATULAIONS to EVERYONE. You're all bloody funny!