"Now James," she says, "can you tell me when you find what I'm doing sexy?"
You nod and say 'sure!'
She starts to take off her stockings a bit, which has the side effect of exposing her panties to your horny gaze.
You tell her that is very sexy!
"No, James," she says in a scolding tone, "I want you to tell me by stroking your cock!"
You stroke your cock for her. Although you find it embarrassing, you find it a turn on also to have her controlling you like this...