Oh great... this isn't going anywhere good... Though I agree that sometimes the "rape" law is abused (and badly), but this might just open the flood gates in the other direction.

This is one of those..."on one hand....the on the other" kind of cases. Is a test of extremes, is she passed out or can barely walk, danger Will Robinson Danger! (and besides if you like to have sex with inanimate objects, get a blowup doll!), having two sips of wine, not so much....

I would suggest a consent form - available at places selling drink, such as pub, clubs, off-license, corner shops ...

To be signed in front of an witnessed by an independent third party - such as the bar staff, shop owner ...

for example
http://www.sex-contract.com

@Steve.. i'm afraid that's a really bad idea.. that means that once a woman "consented" she can't back out. That brings in the ability to coerce the woman (or man) into signing said contract.

Anyone should have the ability to back down/out right up to the point of actual intercourse... at that point, imo, all bets are off.

Your contract would see a rash of rapes where the woman who under th influence sign the contract, but later (maybe minutes later) decide it was a bad idea (maybe the guy turns out to be an ass, won't wear a condom, is rough, etc) and then cannot back out. The guy can essentially rape them with little to no fear of legal reprisals.