Gemara

Question (Rava): If one accepted Nezirus while in a cemetery, must he delay there (the time needed to bow) to be lashed?

He does not ask about one who was warned not to accept Nezirus. He is lashed even if he does not delay, just like a Tahor Nazir who was warned not to become Tamei is lashed, even without delay!

Rather, he entered the cemetery in a chest (that shields from Tum'ah). Someone else removed the bottom, making him (tower over a grave and become) Tamei.

Makos 21a (Mishnah): If a man was wearing Sha'atnez all day, he is lashed only once. If he was warned repeatedly, and he removed the garment and put it on again, he is lashed for each time.

(Rav Bivi): Even if he does not remove the garment and put it on again, rather, he removes his arm from the sleeve and puts it in again, he is liable for each time.

(Rav Ashi): Even if he wears it long enough to remove it and put it on again, he is lashed (for each warning).

Rishonim

Rambam (Hilchos Nezirus 5:19): If a Nazir entered a cemetery b'Shogeg, and after he found out he was warned to leave, he is lashed. This is only if he delayed there long enough to bow, like a Tamei person who entered the Mikdash.

Question (Keren Orah Nazir 17a DH v'Od): The Shi'ur of bowing applies only to the Mikdash. Here, the Shi'ur is in order to leave and return, similar to the time to remove Kil'ayim and put it on again!

Answer (Or Some'ach 6:8 DH v'Nireh): The Rambam obligates only if the delay was also long enough to leave and return, for it is a Safek whether or not we learn the Shi'ur of bowing from the Mikdash.

Rambam (6:8): If one accepted Nezirus while in a cemetery, he is lashed for delaying there. If they warned him not to accept Nezirus, he does not shave when he leaves...

Ra'avad: If he was warned not to accept Nezirus, he need not delay (to be lashed).

Kesef Mishneh: This is the Rambam's intent (our text must be altered).

Or Some'ach: Lashes are for being Metamei himself. Delaying there long enough to bow is like being Metamei himself afresh. He is lashed for vowing Nezirus there only if the warning included not to be Metamei himself.

Rambam (9): If a Nazir entered a cemetery in a chest and someone removed the bottom, making him Tamei, even if he delayed, he is lashed only mid'Rabanan.

Rebuttal (Ra'avad): Rava asked, if one entered in a chest and accepted Nezirus there, and someone else removed the roof, must he delay to be lashed? Surely, if he delayed he is lashed (mid'Oraisa)!

Defense #1 (Migdal Oz): The Yerushalmi says that he is not lashed for delaying. Rava asks whether or not he is lashed mid'Rabanan.

Defense #2 (Radvaz): This is wrong. Rather, the Rambam discusses one who was not warned. Surely, if he was warned and delayed he is lashed!

Kesef Mishneh: It seems that the Gemara is like the Ra'avad. The Rambam must explain that Rava asks whether delaying obligates lashes, or not, i.e. even if he delays he is not lashed, for the tradition (of lashes for delaying) applies only to the Makdish. We are lenient, for the question was not settled.

Rambam (Hilchos Sechirus 13:2): One who verbally muzzled an animal is lashed.

Magid Mishneh: This is because his words do an action. Also one who makes Temurah (tries to transfer the Kedushah of a Korban to a Chulin animal) is lashed because his words caused the Chulin animal to become Kodesh.

Tosfos (Shevuos 17a DH Oh): Rav Bivi agrees with Rav Ashi, who obligates one who wears Sha'atnez long enough to remove it and put it on again. Rav Bivi obligates for a shorter time if he removes his arm and puts it in again. Alternatively, he exempts for a mere delay, for it is Ein Bo Ma'aseh. Alternatively, they discuss what is an Isur worthy of lashes (but one is not lashed).

Mishneh l'Melech (Hilchos Bi'as Mikdash 3:21 DH v'Da): It would seem that one is liable for transgressing passively only if initially he did a forbidden action. However, Tosfos obligates even if his initial action was permitted!

Rebuttal (Beis Meir, cited in Yad Binyamin Nazir 17a DH uv'Chidushei): This is unlike Rashi and Tosfos (Avodah Zarah 64a DH Afilu and DH Rebbi). Also the Rambam (Hilchos Kil'ayim 1:3) exempts from lashes when the action was permitted. He obligates only if he was a Nazir when he entered the cemetery.

Keren Orah (Nazir 17a DH veha'Tosfos and DH Aval): Later, the Mishneh l'Melech himself exempts when the beginning was Ones! Rav Bivi holds that the Mishnah of Kil'ayim is like the opinion that lashes for Lav she'Ein Bo Ma'aseh, and regarding Tum'ah we ask according to the opinion that exempts. Rav Ashi holds that both Sugyos are like the opinion that exempts, and that delaying is like an action.

Question: If one accepted Nezirus while in a cemetery and delayed there, why is he lashed? This is Lav she'Ein Bo Ma'aseh!

Answer #1 (Rosh Nedarim 4a DH v'Chidush and Tosfos Shevuos 17a DH Oh): Delaying is like an action because initially he did an action.

Answer #2 (Rosh and Tosfos, ibid.): The Gemara does not discuss actual lashes, rather, transgressions worthy of lashes.

Answer #3 (Tosfos Nazir 17a DH Ileima and Rambam according to Radal Nazir 17 DH Ayen): Not leaving when he is warned to leave is like an action.

Answer #4 (Rav Ransborg Nazir 17a 9): The above answers are poor. Rather, this is a proof for the Magid Mishneh, who says that a Lav that could be transgressed through an action is Yesh Bo Ma'aseh.

Poskim

Beis Yosef (YD 371 DH v'Chasuv Od (2)): The Kolbo says that if a Kohen entered a cemetery b'Shogeg, and after he was warned he delayed long enough to bow, he is lashed. It seems that this is mid'Rabanan, for it is Ein Bo Ma'aseh.

Lechem Mishneh (Hilchos Evel 3:4): The Rambam obligates mid'Oraisa. If one could fix the situation, but does not, this is like an action.

Note: Most Poskim do not discuss lashes, because nowadays Beis Din does not lash. However, one who transgresses a Lav worthy of lashes is disqualified from testimony.