CalifJim:
Actually, you haven't described the context completely, but I can fill that in for you. Emotion: smile
A: Do you want a cup of coffee?
(B has a cup of coffee right in front of him.)
B: No, thanks. I already have one.
A: Do you want a cup of coffee?
(B is not drinking anything at the moment. However, earlier he drank some coffee.)
B: No, thanks. I've already had one.
