Mom humiliates son (facesitting)
What about this:
Sally got pregnant - maybe because of rape. Or maybe it was normal sex, but the guy dumped her, as soon as he found out, that she is pregnant. Or, they were married, but he run away with a younger, hotter looking bitch.
Anyway, she receives the kid (a son) and raises him up. Of course, she has motherly feelings, but she also has some kind of hidden anger against him. And the older he becomes, the worse it gets, because he looks very much like his father.
So she does different stuff to humiliate him. Like for example, she gives him bad names, when his friends are near. Or she prepares his clothing, so that once he sits down, his pants rip open and everybody laughs about it.
Also, she teases him, by walking around half naked (but all the important parts are still covered). She knows that he wants to see her nude, but she never shows him too much.
One day, she just gets out of the shower, and wraps herself in a towel, when her son walks into the bathroom. He is naked. When she sees his nude cock, she sees that it looks exactly like his dads, and she becomes even more angry about his father - and about him.
She starts to argue with him, because he runs around nude.
"Oh Mom, calm down. You could walk around nude, too. We are at home, no one can see us."
"Yeah, I know what you are trying. You want to see my nude pussy. Hey what about this - I show it to you. Just lay down on the floor and I will show it to you."
He is surprised, but he does as she says. She stands over his face, but since she is still wrapped in a towel and the room is dimly lit, he can't see too much. She gets down in a squatting position and sits on his face. She really enjoys it - until she feels his tongue on her pussy and butthole. She wants to tell him to stop, but it has been some time, since she was licked the last time - and he does it really good, so she keeps the position, until she cums ....
"We have done so much, with so little, for so long, that now we can do almost anything with nothing." - Dave Marcis