Which of the following words does NOT have its letters in alphabetical order?

Let's check the alphabetical order of letters for each word:
* Blank: B(2), L(12), A(1) $\to$ Not in alphabetical order since A comes after L.
* Alloy: A(1), L(12), L(12), O(15), Y(25) $\to$ In alphabetical order.
* Empty: E(5), M(13), P(16), T(20), Y(25) $\to$ In alphabetical order.
* Begin: B(2), E(5), G(7), I(9), N(14) $\to$ In alphabetical order.

Thus, Blank does not have its letters in alphabetical order.