To speak bluntly or directly without softening one's words. It denotes frankness; depending on context it can be seen as refreshingly candid or harsh.
彼は歯に衣を着せぬ性格で、会議ではいつも核心を突く発言をする。
He is blunt by nature and always makes pointed comments in meetings.
上司としては、時には歯に衣を着せぬ指摘が必要だ。
As a manager, sometimes blunt criticism is necessary.
彼女の歯に衣を着せぬ物言いに、部下は驚いたが納得もした。
Her frank manner surprised the subordinates, but they also accepted it.