大言不惭的英文翻译

brag unblushingly

fanfaronade/brag unblushingly 或者 boastfulness
例如：
I'm most unhappy at his boastfulness.
我对他的大言不惭很不高兴。

Unashamedly

barefaced

there are many ways to express 大言不惭.

the word "grandiloquence" has this meaning. you can also say "the man is shamlessly boastful", meaning the man is 大言不惭 (be shamlessly boastful).

one more way i can suggest you is that, when you wanna blame someone, you can say "how dare you say such thing to me?" which means 你竟敢对我大言不惭?