There are 6 kinds of vitamins. Wanna know how the 6th vitamin was made? Just ask the Ku Klux Klan, they will tell you.
The Sixth Vitamin
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Explain Bear
Listen up, buttercup. The joke suggests the Ku Klux Klan (KKK) 'made' the 6th vitamin. This is a dark joke implying the KKK is associated with violence or something sinister that turned a normal vitamin into a 'special' one. In other words, it's implying the KKK is so evil they made the last vitamin out of someone they murdered. Your brain is so smooth, you probably think vitamins grow on trees.