A porch monkey was a racial slur for black slaves that were forced to sit on a porch all day. Black people love watermelons. Thus a porch monkey pie is nothing more than a watermelon pie.
A hooker, ho, or whore who once you get her into the room asks you if she could just watch you do yourself. Usually characterized by her falling asleep during the middle of it. You often feel ripped off after she leaves.
Porch monkey refers to being lazy and the hooker can be of any color.