My idea.
Harvey (now Two Face) walks into a bar where an off-hours cop sits talking to the bartender. He keeps his head down, and has his collar up, obscuring the scarring on his face as he walks past the two. When the bartender asks if he'd like a drink, he replies that he simply needs to go to the bathroom.
The two eye him suspiciously, but then go back to talking. They're talking about Harvey, and the scarring incident which left one half of his face disfigured. The cop cuts a joke about it, and the bartender laughs, and both don't seem to be too high on Harvey.
The cop goes back to sipping his drink, while the bartender is cleaning off some dirty cups and whatnot. After a second, we hear the bathroom door open off camera, and neither of the two seem to really notice until Harvey's shadow is cast over them. The bartender turns to look, and Harvey shoots him in the eye. The cop drops his glass on to the floor, and reaches for his gun, but Harvey shoots him, though not killing him. Cop drops his gun to grip at his injuries.
Harvey walks over to him, dropping the trench coat and removing the hat, and Two Face is revealed. He debates over whether or not he should shoot the cop, then says he'll flip a coin over it. Two Face flips the coin, but we don't see the result. We just see Two Face smiling and hear the sound of him cocking the gun. Fade to black, end credits roll, and I *** inside of my tighty whities.