Matthew Yglesias quotes Dan Savage on the defining characteristics of date rape:

Second, let's define the terms "rape" and "date rape" for all the college sophomores out there: Being pressured into having sex that you regret the next morning does not mean you were raped. Being seduced does not mean you were raped, nor does consenting to sex when you were drunk or high. If someone is pressuring you or seducing you or hitting on you when you're drunk or high, and you try to get up and leave or tell him to stop, and he physically prevents you from leaving and forces you to have sex with him against your will–that's rape. If it happens on a date, that's date rape.

Matt questions the legality of consenting while you're either drunk or high, quoting the Brandeis Student Sexuality Information Service:

First, according to Massachusetts state law, people under the influence of alcohol or drugs are absolutely incapable of giving sexual consent.

To which I'd say: Huh? People under the influence of alcohol are absolutely incapable of giving sexual consent?

If that's the case, there's a whole lot of raping going on. And two drunk adults engaging in sex are apparently raping each other.