Soaps don't make good personal lubricants. Ever. All its going to do is increase friction in the long run, plus its going to dry out the mucous membrane. As a constipation prize its going to sting like all hell. Nope, you want an oil of some sort (say Vaseline, canola oil, coconut oil, olive oil, etc.) or a water based personal lube such as KY jelly or a surgical lubricant. Note that oils are incompatible with most sex toys and with most condoms.