Should he have said Yasa?

It showed that he had learned how to control his temper. He should have shut his mouth and followed directions, and mostly that's what he did. Yassah would have been a sarcastic response and in addition to being inappropriate professional behavior (even in light of the other jerk's behavior), might have drawn him an official reprimand and his goal at that point was to become a doctor, not counter every buffoon that crossed his path. He already said more than he should have because "Are you finished?" was a little defiant, but mostly he allowed his better judgment to govern his action.

Anyway, he was out of line when he contradicted a senior doctor and later, perhaps years later when he himself faced some young smart aleck, I'm sure he realized that.