Originating from the people on "Wheel of Fortune" who either buy a vowel when it is already obvious what the solution is (thus wasting money), or who buy a vowel too early, well before they'd have a chance of solving the puzzle, and thus essentially buy a free vowel for whoever spins next.
"WH _ _ L _F F _ RTUN _"
on the board, and he bought the three E's before guessing! What a vowel buyer!"
To the car in front of you: "C'mon, you vowel buyer! Pull out into traffic and get going! You'll never have a bigger gap!"