I like the idea of "constant reaffirmation".
"I would like your consent to thrust again."
"Yes, I consent!"
"Wonderful. Was that thrust good for you?"
"Yes, I can confirm that as of now, I am satisfied with this sexual encounter."
"Splendid. May I now thrust again?"
"Yes, I consent to that."
"I'm sorry...could you repeat that but a little more enthusiastically?"
Seriously though...it's not something that really breaks down well into codified rules (beyond the obvious). Consent is not always enthusiastic--sometimes people just want to have sex even if they're not super excited about who they're doing it with. Consent (like enthusiasm) is not necessarily verbal.
Everyone wants different things from different sexual encounters--use some common sense and basic empathy in all cases and relax.
"As best as I can figure, 1 person is drunk = any sexual encounter is automatically rape"
That is a bit scary. I get there are extremes but in general this seems kind of blind to how real people are in the real world. Not to say this is particularly healthy, but many people want to get drunk and sleep with someone...it's all part and parcel with a lifestyle common to many people in their young adult years