anything but是固定短语，意思是"根本不是、一点也不、决不"。

【例句】
We'd been warned he was a frail, withdrawn man, but when I met him he was anything but.
有人告诉我们他是一个脆弱内向的人，可当我看到他时，发现他并非如此。

I will be anything but quiet on Saturday night!
星期六的晚上我根本静不下心来！