ONE MUST OBEY HIS HOST [guest: obeying Ba'al ha'Bayis]
Rav Huna brei d'Rav Noson visited Rav Nachman bar Yitzchak's house. They offered him to sit on a bed, and to drink. He did not refuse.
The household: When we offered you to sit on a bed, why did you agree?
Rav Huna: One must do whatever his host says [except for 'leave'. some delete this from the text].
The household: When we offered you a drink, why did you accept it immediately?
Rav Huna: One may decline [an offer from] a simple person, but one may not decline an important person
Erchin 16b (Shmuel): One should not change his lodging until the host is preparing to throw his belongings outside.
Tosfos (86b DH Ein): When they asked why he agreed to sit on a bed, he could not have answered that one may not decline [an important person], for sitting on a bed is haughty and authoritative. He should not have sat, if not that one must do whatever his host says.
Maharsha (Chidushei Agados DH v'Ein): This is difficult. Rav Huna did not refuse even matters of haughtiness due to the obligation to obey the host, and all the more so this is reason to accept the cup! Why didn't he say that he accepted it because one must obey the host? I answer that above, he was able to answer only from laws of Derech Eretz. Here, he preferred to answer based on letter of the law that the Gemara learns from Avraham and Lot [that we do not refuse a Gadol].
Tur (OC 170, citing Maseches Derech Eretz 6:1): One who enters a house must do whatever the Ba'al ha'Bayis tells him to do. Once, guests came to R. Shimon ben Antiferas, and he decreed that they eat and drink, and they were vowing and falsifying, and he lashed them.
Shulchan Aruch (OC 170:5): One who enters a house must do whatever the Ba'al ha'Bayis tells him to do.
Prishah (7): The episode in the Tur is astounding. What "decree" did he put on them? Also, since they vowed not to eat, why did he make them stumble, through feeding them? It is difficult to say that he did not hear them vow. Also, what was their intent, to vow and later eat? Also, how does this prove that one must do whatever the Ba'al ha'Bayis tells him? The episode connotes oppositely, for they vowed and did not want to eat, even though he commanded! I say that long before they entered his house, they had vowed not to eat on another's table, or a similar vow. Now, he decreed that hey eat, i.e. he commanded them to eat. (It says "decreed", for one must obey his host's words, like a decree.) 'When they heard, they violated their vows in order to fulfill his words. This is a good proof of the law! The way Reishis Chachmah brings this episode, it is not difficult. The Tur must explain like I said.
Reishis Chachmah (Perek Derech Eretz, Sha'ar 3 DH Orach): When the guests left, R. Shimon lashed them. R. Yochanan ben Zakai and Chachamim heard, and sent R. Yehoshua to investigate. He found that R. Shimon lashed them for vowing and transgressing.
Taz (3): What proof did the Tur bring from the episode? Perhaps he lashed them for transgressing their vows! I answer that those are vows of Zeruzin (YD 232, which are not binding). Rather, he lashed them for refusing at first. It did not help later to vow.
Mishbetzos Zahav: What is the source that he lashed them for not obeying the host? One may not refuse what a Gadol says! It is difficult to say that they were Gadol like R. Shimon, for he lashed them. This requires investigation. Also, this requires investigation to lash for not fulfilling Derech Eretz. See Rambam Hilchos Mamrim [1:2, who says that Lo Sasur applies also to customs that Chachamim enact. One is not lashed for this, since a Zaken Mamrei is killed for this Lav.] See what I wrote in Petichah Koleles [to OC, Chelek Rishon 42, that one is not lashed [even] mid'Rabanan for matters of Derech Eretz].
Magen Avraham (10): According to Tosfos, why did they ask him why he accepted a drink? He already told them that one must do whatever his host says! I answer that even though one must do it, it is improper to do so immediately, until they insist. However, we immediately do what a Gadol says. Rashi connotes like this.
Birkei Yosef (8): The Magen Avraham holds that it is proper to [initially] refuse [a host's command to do something haughty, unless he is a Gadol]. The Maharsha connotes oppositely, that one does not refuse a Ba'al ha'Bayis. I agree. If Rav Huna sat immediately, this shows that one must heed a Ba'al ha'Bayis without refusing. If he refused, he should not have refused a Gadol, like he did not regarding the cup! Initially he answered that one does not refuse a Ba'al ha'Bayis, to justify his acceptance and not refusing. They asked about not refusing only regarding the cup. Tosfos holds like this. Perhaps they asked about the cup because they were unsure if he accepted immediately due to obeying a Ba'al ha'Bayis, or if this is proper even for one who is not a guest, since he wants to drink. He answered that one does not refuse a Gadol, but we refuse a Katan, unless he is the host.
Mishnah Berurah (16): I.e. even something haughty and authoritative, that the guest would not normally do, due to humility, one should do. If the guest conducts with a certain stringency due to concern for Isur, he need not heed the Ba'al ha'Bayis to transgress. If it is a mere stringency [without concern for Isur], it is good for one to conceal his [good] deeds.
Maharsha (86b Chidushei Agados DH Kol): In a corrected Sefer, the words "except for 'leave'" were deleted from the text. It is not relevant here. Do not explain simply, that if the host says to leave, he need not leave. One cannot stay against the will of the host! Some say that regarding any request he is considered your host, but if he tells you to leave, he is not considered your host.
Bach (6): The Tur brings from Maseches Derech Eretz that one who enters a house must do whatever the Ba'al ha'Bayis tells him to do. Our Gemara says "one must do anyone his host says, except for 'leave'." It seems that this means that any service the Ba'al ha'Bayis tells him to do in the house, he must do it, except for leave. I.e. if he tells him to serve him outside the house, e.g. to go to the market for him, he need not, for this is improper for a guest to go to markets and streets that he does not recognize.
Note: Some say that an Ore'ach (guest) is only someone from another city (Terumas ha'Deshen 72, Shulchan Aruch ha'Rav 333:6).
Magen Avraham (10): Mateh Moshe (290) explains "[one must do whatever his host says] except for 'leave'", that if the host said "leave my house", he does not leave until the host prepares to throw his belongings outside (Erchin 16b). This is correct, unlike the Bach. Even a casual guest may not change [without such reason].
Birkei Yosef (5): Also if he says to do something not so honorable for the guest, he must do it. The Magen Avraham connotes like this. He brings an opinion that exempts only errands in the market, which is not honorable, and he is exempt only because it is not in the house. This implies that in the house, one must do even what is not honorable.
Kaf ha'Chayim (25): The Beis Meir said that he need not pardon his honor. One should judge according to the matter, and pardon only what is not such a great disgrace to his honor.
Birkei Yosef (7): Similarly, one must obey the words of one of the elder sons of the Ba'al ha'Bayis. They are considered like the Ba'al ha'Bayis. Their honor is his honor. The Gemara supports this. It seems that Rav Huna obeyed the words of Rav Nachman's household. It does not say that Rav Nachman told him [to sit...]
Mishnah Berurah (17): Bigdei Yesha says that eating and drinking are excluded. If one does not desire to eat or drink more, and the host insists, he need not, lest it harm him. This does not withhold the host's honor.
Note: Oncee the Gra was a guest, and he vomited out the food back into his bowl. His host saw the bowl full, and insisted that he eat. The Gra repeatedly obeyed, and ate and vomited four times, for it is an Aseh to obey the host, and one must fulfill an Aseh "until he dies" (Hakdamas Bnei Gra to Shulchan Aruch, DH Asaper).
Kaf ha'Chayim (27): R. Chaim [Vital] in Sha'ar ha'Kedushah says that "Ba'al ha'Bayis" is Hash-m. Whatever Mitzvos He tells you to do, do them, except for 'leave my house', like [a Bas Kol (voice from Heaven) said to] Acher (Elisha ben Avuya) not to do Teshuvah. The Shlah brings this. Alternatively, Ba'al ha'Bayis alludes to Chachamim. The Torah authorized them to rule. When there is an argument, one may be stringent and fulfill all opinions, but he may not be lenient unless most Poskim agree. One may do everything, i.e. like everyone, except for Tzei, i.e. to veer from their words and be lenient. This does not depend on your will. The majority must agree.