Loki is not sexist. He knows all too well that women can be powerful. He grew up with Sif, after all. And if their power is not physical strength, then all the more reason - How could he look down on someone whose power comes from the same place as his?
When he called Natasha a “mewling quim”, it was not because he meant it. He was playing the game just as much as she was. He only said it to get a rise out of her.
Submitted by penandpage
Headcanon respectfully rejected.
The point of the scene is that Natasha manipulates him into letting his ego loose, and he ends up slipping up. If he’s playing with her, that means he’s in charge of his emotions at the moment, so he wouldn’t have slipped up.