"Even for the sake of fulfilling a mitzvah (commandment), our Sages of blessed memory have cautioned us not to get angry; even a rabbi with his student or a father with his son. Of course this does not mean that they should not rebuke them. Let them rebuke them, time and time again, but without anger, in order to guide them along the right path, and any anger they express should be only facial rather than [true] anger of the heart."
Only if one can ask him a halachic (legal) question in his area of study, and he can answer, then he is considered a talmid chacham.
Midrash B'Reshis Rabah 48:16: "When you come to a city, behave according to the local etiquette. [From where do we learn this?] Since there is no eating and drinking in heaven, when Moshe went up to heaven [to retrieve the Torah], he did not eat, as it says... 'I did not eat bread nor did I drink water' (Deut. 9:9). But below (on earth), where there is eating and drinking, [it says,] 'And [Avraham] stood over [the angels] under the tree and they ate.'
