不管三七二十一

bùguǎnsānqīèrshíyī
  1. regardless of the consequences
  2. recklessly relying on a hopelessly optimistic forecast

CEDICT

  1. (colloquial) to cast all caution to the wind and act without thinking of the consequences
  2. to cast all caution to the wind and act without thinking of the consequences

Wiktionary

不顾一切，不论是非情由。《醒世恆言．卷一．两县令竞义婚孤女》：「贾婆不管三七二十一，和张婆两个，你一推，我一㩳，㩳他出了大门。」《二刻拍桉惊奇．卷七》：「老妈们心性，见了一百千，算来不亏了本，随他女儿短长也不在他心上，不管三七二十一，欢欢喜喜自出去了。」也作「不管三七廿一」。

重編國語辭典

Entry Composition

1 不管 bùguǎn
  1. not to be concerned
  2. regardless of
  3. no matter
2 三七二十一 sānqīèrshíyī
  1. three sevens are twenty-one (idiom)
  2. the facts of the matter
  3. the actual situation

Related entries

管他三七二十一 guǎntāsānqīèrshíyī
  1. who cares
  2. no matter what
  3. regardless of the consequences