Your enemies will hurl every insult they can think of, Krishna warns. They will mock your strength, your courage, your very name. What could be more painful than that? The question hangs in the air, unanswered — because Krishna already knows the answer. For Arjuna, there is nothing worse.
Notice that Krishna does not describe the insults in detail. He does not need to. The phrase 'avachyavadan' — words that should not be spoken — lets Arjuna's own imagination fill the gap. Every warrior knows the kind of taunts that cut deepest. Krishna simply points to that knowledge and lets it do its work.
This is the sharpest of the social arguments. First came loss of dharma (2.33), then loss of honor (2.34), then the contempt of fellow warriors (2.35), and now — the open mockery of enemies. Krishna has built the case layer by layer, each one closer to Arjuna's nerve.