Irritably tells you how someone does something when they are already close to annoyed. She answered irritably means the manner was short, snappy, or impatient. It often shows in the voice, the face, or a quick gesture, not only in the words. It can be milder than angrily: the person may not be in a full rage, just easily rubbed the wrong way. You use it of people and their actions, not of the thing that caused the feeling. Though actually, English also has irritatingly for that other side — the habit or situation that keeps bothering you. Keep the two seats clear: irritably is how the annoyed person acts.

不耐煩地；暴躁地