Oh, come on. The villain called her that. Loki was trying to diminish and degrade her -- and he failed. She maintained total control of the situation, and by playing on his sexist assumptions and getting him to underestimate her, she manipulated him into giving away his plan. She out-tricked a trickster god. And that's why it was thrilling for the crowd -- not because the villain tried to demean Black Widow, but because she totally kicked his ass. We were supposed to hate him for the "mewling quim" line (which isn't "Whedon-speak" but an archaic British idiom in keeping with the way Asgardians normally speak in the Marvel Universe) and cheer when Natasha made him eat those words.