For the Ladies:

I, (state your name) do solemnly swear that as a woman of the world I will respect and honor my sisters. I will not reveal the secrets of the evening. I understand that violating this treatment will spread bad karma upon my being and may result in increased bloating and cramping. If asked about the happenings of the evening I shall reply:

"Oh, you know, girl stuff, like opening presents and decorating the party with streamers. The brides grandmother was there"

For the Men:

I (state your name) do solemnly swear that as a gentleman of the world I will respect and honor my brothers. I will not reveal the secrets of the evening. In taking this oath I understand that violating it will result in punishment that could include castration by way of a dirty, dull, knife. If asked about the happenings of the evening I shall reply:

"We ate pizza and watched porno movies. The groom got really drunk. His grandfather was there"

It is that simple. We realize total silence is impossible, so a boring alibi is best. Mentioning the presence of someone older usually results in the assumption that they tempered the fun.