To brown-nose is to be extra, extra nice to someone who has power over you — a boss, a teacher, a person who can give you a better job or a better grade — so they will like you, not because you mean the kindness.

To brown-nose拍馬屁 is to be extra, extra nice就是對某人特別特別好 to someone who has power over you對握有你權力的人 — a boss, a teacher, a person who can give you a better job or a better grade像老闆、老師，或能給你更好工作或成績的人 — so they will like you好讓對方喜歡你, not because you mean the kindness而不是真心對他好。

People use it to show they do not respect that behaviour. It is very informal, a bit rude, and it does not belong in a school essay.

People use it人們用這個詞 to show they do not respect that behaviour表示自己不認同這種行為。It is very informal這說法很口語, a bit rude有點不禮貌, and it does not belong in a school essay不適合出現在學校作文裡。

Though actually, the picture behind it is crude: it comes from putting your nose somewhere dirty and brown to please someone above you. English speakers still feel that, even when they say it lightly.

Though actually不過其實, the picture behind it is crude背後的畫面很粗俗: it comes from putting your nose somewhere dirty and brown它源自把鼻子伸進又髒又棕的地方 to please someone above you來討好上位的人。English speakers still feel that英語使用者還是能感覺到這一點, even when they say it lightly即使他們說得很輕鬆。

In class, suck up to or flatter is a safer way to say the same thing.

In class在課堂上, suck up to or flattersuck up to或flatter is a safer way to say the same thing是表達同樣意思更安全的說法。