with gay abandon

With rash, unrestrained impulsiveness, enthusiasm, or zeal. Ever since my brother got that car for his birthday, he's been motoring around at night with gay abandon. The insurgents set upon the town and began firing their weapons with gay abandon.

with gay aˈbandon

(old-fashioned) without thinking about the results or effects of a particular action: Although she was nervous at first, she was soon singing and dancing with gay abandon.

Gay here means ‘happy and without cares’.