Soap on a rope can also be a
gag gift for someone whose
activities lean towards the
illegal. The
innuendo is that if or when the
recipient winds up in
prison, he can use the
soap on a
rope in the
shower. This lets him avoid
dropping the soap and having to
bend over to pick it up.
(If you haven't figured it out yet ... bending over in a prison shower is reportedly not a healthy activity, particularly if the burly guy under the next spigot over has been washing it as fast as he wants ...)