• kṣiptvā — deriding
  Absolutive of √kṣip (to throw). Speech as projectile — Kṛṣṇa has 'thrown' the mocking words first; the bāṇas follow. Gauḍīyas note: in a Vyāsa-narrative, the verbal blow always precedes the physical one — speech is the first weapon, last refuge.
• virathī — chariotless
  From vi- (without) + rathin (chariot-warrior). A status-stripping word in dhanurveda — once virathī, a warrior has been functionally defeated. Kṛṣṇa first removes the chariot, then the head: rank dismantled, then life.
• ratha-aṅgena — with His Sudarśana disc
  Compound: ratha (chariot) + aṅga (limb, wheel). 'Wheel-of-the-chariot' — a poetic name for Sudarśana that recalls the moment in BG 1 when Kṛṣṇa, weaponless by vow, threatened Bhīṣma with a chariot-wheel. Sudarśana is the Lord's vow-keeping device.
• avṛścat — He cut off
  Imperfect of √vraśc (to cut, to fell). The same root used for felling trees in the forest. The Bhāgavata treats Pauṇḍraka's death with the matter-of-factness of timber being cut — there is no elegy. The man who had not earned a name has not earned a lament either.
• vajreṇa indraḥ — Lord Indra with his thunderbolt
  Compound simile: Sudarśana is to Pauṇḍraka as vajra is to mountain, Kṛṣṇa is to action as Indra is to action. Gauḍīyas note that Indra is here the upamāna (compared) and Kṛṣṇa the upameya (compared-to) — the standard Vaiṣṇava ordering, Bhagavān as original of all simile.

• What false identity in me cannot survive sustained contact with Kṛṣṇa?
• Am I willing to let that part be cut?

Indra cuts a peak from a mountain with the vajra, and the mountain has no recourse but to be smaller; so the head of Pauṇḍraka falls from his shoulders by Sudarśana. The simile is borrowed from Vedic cosmogony because the event it images is cosmogonic — the false sovereign is unmade.