Peremptory comments are like orders. If you say something in a peremptory manner, you want people to stop what they’re doing and do what you say. Peremptory comments put an end to a discussion, and that’s final!
The word peremptory comes from the Latin peremptorius for “decisive, final.” Trace it further and find that peremptor means "destroyer," from perimpere for "destroy, cut off.” Basically, peremptory commands destroy the conversation. They are given with an air of authority, and they are often barked. In the courtroom, peremptory orders are not open to appeal; they’re final. Outside of the courtroom, a peremptory manner is just plain rude.