Being 'drunk' is completely subjective.
The laws are against certain amount of drink having being consumed whilst operating a vehicle. For one person, it might not be enough to make them drunk. For another person, they might be completely wasted. Regardless, it's still against the law for both of them.
So 'Drunk Driving' is a more stupid term when you think about it. It's misleading.
Although being drunk is subjective, the laws have made it clear that there's a threshold. In my state, if you have a BAC of .08 or more, you're considered drunk whether you're wasted or not does not matter under the law.
"Drink driving" implies you're driving with a drink in your car. Drink is a noun to me. It's like the lawmakers thought, "Hey, since we're setting an abstract limit as to when a person is drunk or not, we're going to save ourself from subjectivity in the public's eyes by calling it 'Drink Driving'."
Regardless, DUI is used in court proceedings and the like here. Drunk driving is more of a layman's term.
Either way, the "you're stupid" wasn't serious. I was just interested in the difference.