don’t tell me —(also: never tell me) is used to express incredulity, disappointment, or dismay:
- “Don’t tell me we’ve got to go through that again,” said one executive member in an audible groan.
say no more—you need not add anything (said when in the course of a conversation one party communicates his total understanding of smth.):
- I hadn’t thought much about this post, actually, as a piece of writing. But say no more: I know well enough not to argue with such a lovely woman.
Note: The expression does not correlate in meaning with the phrase it goes without saying—it is too obvious or well known:
- It goes without saying that a good first impression is critical.
See also: don’t mention it / don’t talk to me about it.