A different definition than the goth/raver hybrid.
A secret act carried out that is so embarrassing or awful that you will die before telling anyone what you did...even your closest friends.
This usually falls under the whole, "It sounded like a good idea at the time" deal. Luckily, there are no witnesses.
Destroying something by accident, the biggest lie one would ever tell or a sexual escapade that would bring down the furious wrath and ridicule of one's friends. Forever.
I will never speak of my sex-fest I had with the siamese twin midget transexuals I met at the circus. Although I enjoyed it, I'm keeping this story as a graver.