There are no characters under the age of 18-years-old in this story.
If she deliberately flashed him, he'd love to return the favor and deliberately flash her too.
His reward for appreciating his mother, whenever she slowly and sexily crossed her long, shapely legs like that, expecting her to do so, she always flashed him a patch of her white, sheer, bikini panties.
'I love seeing flashes of my mother's panties,' he thought while enjoying the view.
When she mindlessly crossed her legs ever so slowly as if she was lost in thought and was alone in the room, he wondered if she knew she was flashing him her panties and had flashed him her panties.
He wondered if she forgot that he was sitting across from her. She'd never give me incestuous sex,' he said while sadly lamenting his sexual frustration that he could no longer hide from his mother.