I still don't get what's going on entirely, but my main question is this: How the hell do people find people like this to hang out with?

If I agree to be a DD then I'll make sure to get the person who is drinking home safely. Leaving them in a car by themselves is not safe. If any of my friends agreed to be a DD they'd NEVER leave me in a car on my own. You need new people to hang around. The rest of this convoluted story is pointless.