The saying in French for ‘don’t pull any punches’, or to ‘not mince words’, or to ‘take the gloves off’ is:
ne pas prendre de gants…
… which literally means to ‘not put on the gloves’. That is to punch someone without gloves on and anyone who understands boxing will know that this means a greater likelihood of substantial damage to the recipient.
Here it is in a French sentence:
Valérie n’a pas pris de gants pour lui dire ce qu’elle pensait.
Valerie did not pull any punches when she told him what she thought.
Valerie did not mince words when she told him what she was thinking.
Learning idioms and proverbs and sayings is a great way of improving your French.