Taken from Wikipedia's entry: http://en.wikipedia.org/wiki/Principle_of_charity
In Objectivism, the main principle for dealing with others is justice, not charity. Charity (in rhetoric), as described in the Wikipedia article cited in the question, isn't entirely different from or opposed to justice. Certainly if a speaker is ambiguous in his terminology such that there are multiple possible interpretations, then justice would imply acknowledging that fact and responding to both (or all) significant and credible interpretations. But justice would not imply "bending over backwards" and giving the maximum possible "benefit of doubt" to a speaker who isn't very precise and has expressed sufficient potential meaning to warrant a critical response. From the perspective of justice, a responder (Objectivist or not) is under no obligation to help a speaker to tighten his formulations to make the speaker's intended meaning more clear. An Objectivist may want to help, in the interest of spreading rationality; but if the speaker said something that could reasonably be understood by others in a way that an Objectivist would want to challenge, then (by justice) an Objectivist should challenge it. A is A; the speaker's words express what they express. At most, a responder acting on the principle of justice should mention "a more charitable assessment" of a speaker's words if the speaker has left the door open to it -- but "a less charitable assessment" is also fully warranted (by justice) if the speaker has also left the door open to that interpretation.
It is also very often the case that follow-up responses by the speaker are available to him. Any speaker who believes he may be a victim of injustice and/or misunderstanding is perfectly free in such cases to speak up about it. But an Objectivist would not grant him the unchallenged prerogative to rewrite reality by claiming, in effect, that words do not have an exact meaning. Again, A is A; words express what they express. It is the speaker who bears the burden to correct his words if they didn't quite come out as he intended.
Update: Improper Questions
In a comment, the questioner quotes from Ayn Rand's answer to a question about identity versus free will in Ayn Rand Answers. Ayn Rand's discussion spans pp. 151-153 (two and one-third pages) and probably will need to be read very closely many times to understand exactly what she is saying. The excerpt quoted by the questioner comes from the very last paragraph of that discussion. The first paragraph (p. 151) opens the discussion as follows:
It's almost blindingly self-evident that the philosophical fundamental being ignored here is the Law of Identity. This is a good example of what questions you need not bother answering, since they contradict philosophical fundamentals. The guideline for anyone tempted to ask such a question is: Do not rewrite reality. On what grounds did someone decide that choice contradicts identity? That is an arbitrary construct of determinism.
The rest of Ayn Rand's discussion elaborates on these points in considerable detail (for more than two pages). A key observation on p. 153 explains:
... a conscientious person might feel it's up to him to answer impossible questions. The unstated assumption behind this attitude is that nobody could be as dishonest and irrational as some of these philosophers are....
When Ayn Rand cautions, "Don't give anyone the benefit of the doubt if your first impression is that he's irrational," she apparently means that one should examine the issues and formulations more closely to identify their philosophical essence, then pronounce judgment on those essentials. Earlier, on p. 153, she describes the process as follows:
This is what I mean by reducing questions to see whether they correspond to or contradict basic axioms [such as existence and consciousness].
Ayn Rand's two-and-one-third-page discussion is certainly well worth reading in contrast to the "principle of charity." The book also contains many other questions that Ayn Rand evaluated as improper or dishonest. They can be located by looking up "questions, improper," in the Index.