The C-word

ISAAC: Rowan, I know the C-word. [SUSAN's hair stands on end but she manages to refrain from commenting.]

ROWAN: There is no C-word, Isaac.

[SUSAN, to herself: Phew.]

ISAAC:  Yes, there is.

ROWAN: No, there isn't. There's an A- word, and a B-word, and in F-word, but there isn't a C-word.

ISAAC: Yes, there is. I've said it.

ROWAN: And an S-word ... and a ... what is it, then?

ISAAC: Ccccccccstupid.