This black Sap Cap is a weapon the bullies at school won’t ever see coming. It looks like a normal black cap, but it incorporates the same material as in a Blackjack (what the cops use as a baton) to quickly whip off your cap and crack a guy’s skull in half. Then simply put your cap back on and leave no evidence at the scene of the beating.

From the product description:

This standard baseball cap can be used as a blackjack or sap. Just use the bill as the handle and the cap as an impact weapon. The secret of the Sap Cap is the pocket of a unique impact material that is 110% the density of lead and will not rust. Velcro adjustment.

The best part of the Sap cap is that it only costs around $30, so you can get a deadly weapon and save your money all at the same time.

Source: http://www.crunchgear.com/2009/05/02/sap-cap-offers-self-defense-at-the-drop-of-a-hat/