Free Shipping on all U.S. orders at Freshpair.com. The Calvin Klein Knit Slim Fit Boxer, from the Calvin Klein bxr-matrix collection, takes an innovative approach to boxer sizing so you know just what you’re getting into. This Calvin Klein boxer is slim fitting with a lower rise and shorter legs so it fits great under skinny jeans. The Calvin Klein Knit Slim Fit Boxer is the perfect choice for active guys seeking a tailored fit.