Ask the bride to leave the room for a few minutes. Get one of the girls to hold up a needle. Ask the bride to come back into the room and try to thread the needle. The girl holding the needle needs to keep moving it around a bit so that the bride cannot thread it.
The fun part is when the bride leaves the room; tell all the guests that the conversation about to occur between the bride and the person holding the needle, actually is the conversation that will occur between the bride and the groom on their wedding night! Between all the “stay still”, “I can’t get it through the hole!” and “darn, missed again!” that goes on, the laughter will hit an all time high.
Of course, the poor bride won’t have any idea what the big joke is until you have all had a blast! Just make sure she is an easy going gal or she may get embarrassed.