as bold as brass 厚颜无耻；极其胆大妄为的；极为粗率无礼的

【例句】
It is hardly believable that such a pretty young lady is as bold as brass.
真是难以置信这样一位年青漂亮的太太竟然如此厚颜无耻。

They walked in holding hands, as bold as brass.
他们竟然手拉着手走进来，真是胆大妄为。