Personalized Pi Day Funny Math Pie Slice Women's V-Neck T-Shirt. Funny every day is a good day for pie Pi Day Women's V-Neck T-Shirt - Black math shirt. 5.0 oz., 100% pre-shrunk cotton Athletic Heather is 90/10 cotton/polyester 1x1 rib collar with mitered v-neck Shoulder-to-shoulder taping Ladies' fit