Key TakeawaysFedEx shares plunged 15% Friday, a day after the package delivery giant missed quarterly estimates and reduced its forecast as it faced what CEO Rajesh Subramaniam called a "challenging Q1 demand environment," especially in the U.S.The company pointed to weakness in the industrial economy impacting business-to-business revenue.FedEx also said it faced a decline in priority shipping volume and growth. FedEx (FDX) shares plunged 15% Friday, a day after the package delivery giant missed quarterly ...