Dangerous for all parties involved. Being out in the open with no safety belt, no crumple zones, a bicyclist can be easily killed in an accident. Drivers attempting to swerve out of the way can cause a greater accident with other vehicles, not to mention the possibility of killing a bicyclist. Add to that, the hypothetical of riding a bicycle while drunk, you've now just worsened the problem.

Moral of the story: don't drive drunk, don't ride a bike drunk. Ideally, don't get drunk at all, but if you do, don't operate any kind of vehicle.