Drink Driving impares the following things
Slows down your brain functions. This means you're slower to react and make decision.
Reduces your ability to judge your speed and distance, so you don't notice how close other cars and objects are to you.
Makes you more confident than you would be normally, leading to dangerous and reckless driving.
Takes away your ability to multi-task. Suddenly it becomes a lot harder to concentrate on steering the wheel, controlling your speed and taking in your surroundings.