The editor responded to the arrogant reader's letter in a sarcastic tone.

sarcastic 是形容词，由名词 sarcasm（讽刺）加上形容词后缀 -tic 构成。sarcasm 来自希腊语，原意是"撕肉"，引申为"尖刻的讽刺"。sarcastic 用来形容言语或语气"讽刺的、挖苦的"。