“Hey what’s in this drink” was a stock joke at the time, and the punchline was invariably that there’s actually pretty much nothing in the drink, not even a significant amount of alcohol.
See, this woman is staying late, unchaperoned, at a dude’s house. In the 1940’s, that’s the kind of thing Good Girls aren’t supposed to do — and she wants people to think she’s a good girl. The woman in the song says outright, multiple times, that what other people will think of her staying is what she’s really concerned about: “the neighbors might think,” “my maiden aunt’s mind is vicious,” “there’s bound to be talk tomorrow.” But she’s having a really good time, and she wants to stay, and so she is excusing her uncharacteristically bold behavior (either to the guy or to herself) by blaming it on the drink — unaware that the drink is actually really weak, maybe not even alcoholic at all. That’s the joke. That is the standard joke that’s going on when a woman in media from the early-to-mid 20th century says “hey, what’s in this drink?” It is not a joke about how she’s drunk and about to be raped. It’s a joke about how she’s perfectly sober and about to have awesome consensual sex and use the drink for plausible deniability because she’s living in a society where women aren’t supposed to have sexual agency.
The song has a line where the girl asks what’s in her drink. You can interpret that however you want.
Not if you want to be accurate:
I’m not debating that at all. I’m merely pointing out that we live in a post-Cosby society.
She knows exactly what’s in the drink.
The context is that she doesn’t want to leave.