"Some practical jokes" joke
Cheap plastic rings
A groom buys the engagement ring at a jewelry store. As the groom enters the room, we "have been talking about" the news that says the jewelry store he just went to is being investigated for selling plastic diamonds to unknowledgeable customers. This didn`t work too well but maybe if you have better actors in your group it would.
I`ll just call my lawyer about this
Another on that I have seen pulled is to have someone speak out at the time the minister asks, "If anyone has good reason why these two should not be married, speak now or forever hold your peace."
They had a pregnant lady stand up and say, "Oh, never mind! I`ll just call my lawyer!" It rattled the groom`s mother so much that she fainted.
A secret pregnant lover
At the rehearsal dinner for my boss` daughter and son-in-law-to-be, a loud eight-months pregnant teenage girl suddenly appeared at the back of the room screaming ten minutes worth of curses that would befall the groom if he didn`t marry the pregnant girl like he promised. It was set up by the boss` wife, and I am told that the groom very nearly burst into tears protesting his innocence.
Not enough votes...