Kaylee: Come on, admit it, it’s true.

Simon: No, I won’t, because it’s not. I use swear words like anybody else.

Kaylee: Oh, really? See, I never heard you. So when is it you do all of this cussin’? After I go to bed, or…

Simon: I swear when it’s appropriate.

Kaylee: Simon, the whole point of swearing is that it ain’t appropriate.

(Inara walks in)

Kaylee: Hey, there, Inara! Heading off for some glamorous romance?

Inara: Lets hope so. See you two tomorrow. Don’t let Mal get you into too much trouble while I’m gone.

Kaylee: Bye, now. Have good sex! (off Simon’s look) What?

Firefly — Episode 7 — “Jaynestown”