Press FLAG to start game. Press the blue button to play as the burger. Press the red button to play as the hotdog. Press the SPACE key to move. Once you press one of the buttons, the other runner is programmed to run as fast as it possibly can. Be quick. You can hold the SPACE key to run faster.
Thanks to DJ_Melonzzz for creating the original RACE HIM (I didn't remix it on this one, though.)