[not a teacher]
That was a start.
Supposing, I've had a talk with someone and not satisfied with it. What should I say to show my discontent and trying to sound polite at the same time?
Mmmm. That was a "nice" talk... (something of the kind)
Thanks in advance/
You could perhaps say that the discussion was not as productive as you had hoped, or that it did not go the way you had hoped. If you're being polite, you should invite the person to have another discussion or meeting so that you can talk about why you weren't satisfied with the previous discussion.