"S my P" is a discrete way to let someone know that you Shit your
Pants. It is for
people who are either ashamed of their activity or want to make light of the situation.
However, "S my P" is not to be confused with "S my D," which refers to Suck my Dick or "S my C," which refers to Suck my
Clit. This should be easy to keep straight in your head because no one says, "Suck my Penis."