Not mincing one's words

In the past, the comedies in the theatre were quite unsparing - even high statesmen and politicians could be ridiculed and criticised. To prevent the actors from being punished for this, they hid their faces behind masks.

In the early days of theatre, however, masks did not yet exist and therefore actors simply used a sheet of paper.

So if you don't mince your words (or in German "you do not hold a sheet of paper in front of your mouth", you speak your mind without hesitation, you speak without embellishment or say something directly, even if it is unpleasant.