Agree to disagree
The phrase "agree to disagree" typically refers to a situation where each of two parties possess opinions which contradict each other but they have agreed (often implicitly) not to enter into conflict over the issue.
Entering into conflict over an issue is not the same thing, however, as expressing one's side of a disagreement. This distinction is often blurred when one party wishes to suppress further dialogue: "I thought we had agreed to disagree on this" is difficult to respond to, as any response other than acquiescence carries an implication that one has acted in bad faith.
see also: Aumann's agreement theorem