it's every man for himself idiom
人不为己，天诛地灭（指在某种特殊场合，每个人都会尽力维护自己，而不会帮助他人）
something that you say that means that everyone in a particular situation is trying to do what is best for themselves and no one is trying to help anyone else
It might be a civilized place to shop at other times, but come the January sales, it's every man for himself. 人们在购物时通常都能保持风度，一月大减价例外，这个时候，人不为己，天诛地灭。