From Longman Dictionary of Contemporary Englishin (your) shirtsleevesin (your) shirtsleevesDCwearing a shirt but no jacket → shirtsleeve
Examples from the Corpus
in (your) shirtsleeves• Men in shirtsleeves and women in summer dresses were strolling around the airport and ice-cream vendors were doing a brisk trade.• He was in shirtsleeves, his jacket crumpled on a chair beside him.• I shivered with the cold and realized I was in shirtsleeves.• Most of the men were working in their shirtsleeves. 