Baffling Bra (21st Century Silks) by Empire Magic
The magician ties two handkerchiefs together, then gives to a lady, who hides the knot just inside her blouse collar or in a shirt pocket. The magician vanishes a third silk and claims it will appear tied between the two hankies the lady is holding. When the hankies are pulled out, instead of the vanished third silk, there's a bra tied between them! A comedy classic.