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”