From Longman Dictionary of Contemporary Englishbe (walking/treading/skating) on thin icebe (walking/treading/skating) on thin icePROBLEMto be in a situation in which you are likely to upset someone or cause trouble I was on thin ice, and I knew it. → thin
Examples from the Corpus
be (walking/treading/skating) on thin ice• It had been granted grudgingly and she knew she was on thin ice as far as her superiors were concerned.• He was on thin ice before. 