A dildo that has some form of adhesive, that literally allows it to be slapped on, over the woman's vagina. The infamous danger being it detaching in a compromising position, such as pegging.
The sound that occurs when being slapped across the face by a big penis. Usually the head of the person being exposed to the slap slap will move from right to left during this procedure.
His penis was so big that I could literally hear a "slap slap" while he was hittingmy face with it.