Choose your weapon. Some like the classic long, yellow and skinny, while others prefer the durable black with a taped grip. Still others want to imitate Bam Bam and haul out their over-sized pink whiffle club. Whatever your style, choose a bat that's durable and comfortable for you.
Prepare your whiffle ball bat by cutting off the top with a hacksaw. This will enable you to load the bat with an assortment of performance enhancing materials.
Buy a bag of bouncy balls and insert them into the opening (or the bottom) of your bat. Keep adding them until they reach the very bottom, filling the bat, then tape the bottom and handle with electrical or duct tape.
Use tennis balls for big bats. Cut off the top and shove as many tennis balls as humanly possible into the bat. Tape over the top of the whiffle ball bat with duct tape once the inside is completely full.
Load it up with ball bearings. Take a sturdy whiffle ball bat (preferably one made of very durable plastic) and fill it up with the above concoction. Seal the bat tightly with layers of duct tape to ensure that nobody loses an eye.
Wrap it in electrical or duct tape. Wrap the barrel of your whiffle ball bat generously with tape, keeping the layers even and smooth. This should give it just enough weight to be dangerous.