glad rags
From Longman Dictionary of Contemporary Englishglad ragsglad ragsold-fashioned informal your best clothes that you wear for special occasions → gladExamples from the Corpusglad rags• Put on the glad rags and go out and party, after that?• She changed out of her glad rags, tugged on old jeans and a sweatshirt and drove out to his house.• Her sister-in-law's glad rags were not very glad.