@extremo777: "Bạn" means "Friend", and "Bạn thân" means "Good/Close/Dear friend".
Asmodeus thinks these two concepts mean an oath of blood (or in the "dear friend" case, an oath etched into the soul) to share joys and sorrows, and to give one's life for Iruma, which enrages the class at first because they think Iruma is making them unconditionally swear an oath to him (and not the other way around).
In the second half, Iruma explains that "friend" is just someone you respect and have bonds with, and are happy to be around; with "dear friend" being someone you have even closer bonds with. Finally they just talk about whether they consider different people friends or not, leaving on a cliffhanger of Ameri-san being... [to be continued]