As a result of a conversation in the pet peeve threads, Herkles asked for some examples of useful French idioms that could replace "ouais".
It depends how posh or crass you want to sound.
If you're playing a lower class PC or your noble is deliberately affecting lower class manners to be offensive and shocking, "Ouais" is of course fine. (And this is perfectly valid RP -- nobles affecting lower class manners to be shocking is a tradition as old as the Roman Republic and the Clodians, if not even older).
If you're trying to sound posh and well-educated, but don't want to use a boring simply "oui", then there's:
* "En effet" (literally "in effect"), which means
indeed, or
that is so. (Not to be confused with "en fait", which means literally and idiomatically "in fact").
* "C'est vrai", or simply "Vrai", which means
that's true.
* "Certes oui" or simply "Certes". (I use this one all the time.) This, depending on context, is closer in meaning to
admittedly,
indeed or
certainly.
http://dictionary.reverso.net/french-english/certes* If you want to say "still or "always" there's "Toujours" (still/always); or even the more dramatic "A jamais!" (literally "to never", idiomatically "forever") -- useful for making declerations of ever-lasting love.
Then there's the special case of "Si", which is used to make an affirmation in the face of a negation. For example: "You didn't do your homework, did you, Tommy?" "
Si, si, I did, mother!"