overstep the mark太過分。overstep有超出某個限度的意思，而mark是標記，在這裡指可容許範圍的標記，所以overstep the mark就是指「超過可容許的範圍」，也就是「太過分"。overstep the line也有同樣的意思。
看看老外聊天時怎麼用overstep the mark：
Emma: What are you doing? Writing a letter?
Bart: Sort of. It's a sorry note to Linda.
Emma: What did you do to her?
Bart: We had a fight yesterday, and what I said overstepped the mark Emma: Maybe you can buy her a gift and give it to her with that sorry note.
埃瑪：你在幹嗎？寫信嗎？
巴特：差不多，這是給琳達的道歉信。
埃瑪：你對她做什麼了？
巴特：我們昨天吵了一架，當時我說的話太過分了。
埃瑪：也許你可以買份禮物，和道歉信一起送給她。
overstep the mark例句精選：
I really feel like you overstepped the mark when you started criticizing John's ability as a parent.
當你開始批評約翰作為父母的能力時，我真的覺得你越界了。
The local city council has overstepped the mark by imposing this steep new income tax on its residents.
地方市政局對居民徵收這項新的高收入稅，已經超出了標準。
He has really overstepped the mark this time, shouting at the referee like that.
他那樣衝裁判大喊大叫，真是太過分了。
拓展學習：
outrageous 令人難以接受的
detestable 可惡的
moderate 不過分的
go too far 太過分
the last straw 忍耐的極限
be off-limits 不可逾越；禁止入內