The author is arguing that it’s not rapey, because the only reason she wants to get home is because of social concerns about her respectability. Well, that was EXACTLY the attitude that most predators had: she really WANTS to; she only SAYS she doesn’t because she’s afraid of what people think. Of course, her choice to weight societal judgment is hers to make, and can’t be invalidated. Let alone that those concerns may not merely be external: the song is quite wrong in its suggestion that date-rape drugs weren’t a worry, and of course, the matters of birth control, sexually-transmitted disease, personal morality, the preservation of virginity, etc.
But there is a perfectly non-rapey interpretation that this touches on, that he’s NOT pressuring her for to go all the way, merely to take the excuse nature has given her to not worry about getting home for the sake of “respectability.” He’s arguing, “Look no-one’s going to expect you to drive home in this.” In this context, “Hey, what’s in this drink” isn’t about roofies (or Spanish Fly, or legendary date-rape drugs), but simply her way of starting to concur with him: “The alcohol is hitting me harder than I expected. I should drive drunk!”
If they were actually going to have sex, certain lines don’t make sense. “My maiden aunt’s mind is vicious” implies that he maiden aunt’s would think they did more than they’re doing. Lastly, of course, if this is all concern about intercourse, they could have sex and then have her go home. No, it’s about making out.
*I should NOT drive drunk.