Knife Owners' Protection Act of 2018 This bill permits an individual to transport a knife between two places (i.e., states) where knife possession, carry, or transport is legal. A knife must be securely stored during transport, unless it is an emergency knife designed to cut seat belts. It repeals provisions, commonly known as the Federal Switchblade Act, that prohibit: (1) the introduction into commerce, or transport or distribution in commerce, of switchblade knives; and (2) the possession, manufacture, sale, or importation of ballistic knives. Finally, it amends the federal criminal code to eliminate two provisions—one that restricts the mailability of switchblade knives and one that restricts the mailability of ballistic knives.