You could have just said no.

[His first sentence remains quiet and even. As he continues to speak he allows himself to show the anger he feels and his voice rises.]

I don't know what your skills are, but I do know that you won't shut up about how mages are treated. And here I am, clearly open minded to solutions that involve magic and you do nothing but mock me for it repeatedly.

[Alistair is honored to be a Grey Warden and any other day would be dedicated to finishing a task. At least that was before he was paired with Anders.

He turns his back to leave the way they came, taking his supplies with him.]

I'm done. Have fun with the darkspawn for me.