When a laborer is occupied in his work he is not obligated to stand up for a Talmid Chacham.
When the people bringing Bikurim enter Yerushalayim all of the laborers stand up for them and wish them Shalom.
The Mitzvah of standing up for a Talmid Chacham does not apply in a bathroom or in the inner room of a bathhouse. (1)
One may not ponder words of Torah in a bathroom or in the inner room of a bathhouse.
If one sees a Talmid Chacham coming he may not close his eyes so that when the Talmid Chacham reaches within 4 Amos he wont see and will not have to stand up for him.
One must stand up for a Talmid Chacham when he reaches with 4 Amos; if he is a Rav Muvhak he must stand up as soon as he is within sight.
Abaye stood up for R. Yosef as soon as he the ears of the donkey that he was riding came into sight.
A Talmid Chacham should try to go out of his way so that people will not stand up for him and if he do so he will merit a long life.
Isi Ben Yehudah says that one must stand up for an elder man even if he is an Am ha'Aretz.
R. Yochanan stood up even for elder Nochrim because they have lived through many events; Rava didn't stand up for them but honored them somewhat.
A Talmid may only stand up for his Rebbi once in the morning and once in the evening so that we will not honor a Rav more than Hashem Yisbarach.
A Talmid Chacham who does not stand up for his Rav is a called a Rasha, he will not merit a long life and he will forget his learning.
If a son is the Rebbi of his father it is a Safek if they must stand up for each other.
If a Metzora or a person holding a stone with Tzara'as is sitting under a tree he is Mitamei anyone who is under the tree. (2)
If a Metzora or a person holding a stone with Tzara'as is walking under a tree he is not Mitamei anyone who is under the tree.
If a Rav is riding on an animal one is obligated to stand up for him. (3)
A person is obligated to stand up for a Sefer Torah; it is a Kal va'Chomer, if one must stand up for those who learn Torah certainly one must stand for a Sefer Torah.
R. Elazar says that a Talmid Chacham does not have to stand up for his Rebbi when he is occupied in Limud ha'Torah. (4)
Women are Patur from time bound Mitzvos Aseh.
A BIT MORE
1. However in the outer room of the bathhouse where everyone is dressed one must stand up for a Talmid Chacham.
2. A Metzora is only Mitamei when he is sitting, however the person who is Tahor who is under the tree becomes Tamei whether he is standing or sitting. The stone with Tzara'as also is only Mitamei if the person who is holding it is sitting.
3. Even though the Rav is sitting since the animal; he is riding on is standing he is regarded as standing and one must stand up for him.
4. However Abaye cursed those that follow this opinion of R. Elazar.
STANDING UP FOR THOS THAT BRING BIKURIM
R. Yochanan says that laborers stand up for those that bring Bikurim and not for Talmidei Chachamim. Rebbi Yosi Bar Avin explains because a Mitzvah b'Sha'atah (in its proper time) is very precious. How can it be that a Mitzvah b'Sha'atah is greater than Talmud Torah which is equal to all of the Mitzvos? The Pnei Yehoshua answers that the people who are bringing the Bikurim are occupied in the Mitzvah at that time while a Talmid Chacham is not always occupied in Limud ha'Torah. Therefore the laborers do not stand up for a Talmid Chacham because maybe at that time the Talmid Chacham is not occupied in Limud ha'Torah.
AN UNWORTHY TALMID CHACHAM
A person is obligated to honor a Talmid Chacham and stand up for him. However if the Talmid Chacham is a child the obligation to stand up for him does not apply. If the Talmid Chacham is a confrontational individual and causes Machlokes that is not l'Shem Shamayim there is no obligation to stand up for him. (Ri'az)