Idioms of bold in English

be/make so bold (as to do something)

(formal) used especially when politely asking a question or making a suggestion which you hope will not offend anyone (although it may criticize them slightly)

If I may be so bold as to suggest that he made a mistake in his calculations…

(as) bold as brass

(informal) without showing any respect, shame or fear

She marched in here, bold as brass, and demanded a pay rise.