have a field day

Từ điển Oxford Advanced Learner 8th

have a ˈfield day idiom
(NAmE, BrE)to be given the opportunity to do sth that you enjoy, especially sth that other people do not approve of
•The tabloid press had a field day with the latest government scandal.
•Shoplifters appear to have had a field day at the January sales.
Main entry: ↑field day_idiom