67. Quirks
While her teasing always startles him, he understands that she really has no other way to motivate him—and anyway, adrenaline is most effective if it is used correctly.
Also it is because in the way the only galvanizing force she had was a gun; and her aim is good, uncannily so. She doesn't miss, so for her this kind of pretending is almost a joke.
Roy also understands the role of women in the military, and Hawkeye's is obvious: to intimidate.