You tie two scarves together and place them in the middle of a spectator's hands. With the ends hanging down at the sides, you then ask two spectators to pull on these ends to make the knot disappear.
But when they pull on it, in the middle of these two scarves appears a large pink bra, which will produce a slight discomfort from the spectator, but above all an explosion of general laughter.
A not very fine gag, it's true, but so funny that you can't do without it.
Ideal to do at a wedding!