Personalized Worlds Best Concert Mistress Long Sleeve T-Shirt. Worlds Best Concert Mistress Long Sleeve T-Shirt - White a perfect gift for the best Concert Mistress in your life. Pre-shrunk 100% cotton 6.1 ounce long sleeve t-shirt. Double-needle stitched neckline and sleeves. Quarter turned. Shoulder-to-shoulder taping. Adult: S, M, L, XL, 2XL, 3XL