At the time this song was first released there was no such thing as a "roofie"....
you could "slip someone a mickey" (a.k.a. choral hydrate)... Of course, that did make them sleepy, although relatively slowly. It also didn't have the amnesiac effect of a date rape drug.
"What's in this drink?" is more likely related to the fact that it was expected that women's drinks were typically made weaker... most people believed that a dainty woman wouldn't like a strong "man's" drink, and if she did it was implied that she was an alcoholic. So I would take the line to mean: "what are you trying to do, get me drunk?"
{just an fyi: My grandmother owned a bar, and she said that there was a time when even women who hung out in bars wouldn't be caught dead doing shots, or even drinking things that were considered masculine, like a whiskey sour or a martini. The novelty martinis were invented so women would feel more comfortable ordering them.}
I've been date raped, and believe me, there was no playful banter, no flirtaceous fun, no asking, really, at all. He didn't try to talk me into it, or convince me that we should. He simply made up his mind that we would be having sex, and from that point on, nothing I said mattered. There were no cute comebacks, or witty retorts. Actually, he said very little- "stop fighting... it'll feel good if you stop fighting it" (it didn't) ... "Every woman I'm with says I'm like a god..." (he wasn't) .... and a few other similar self-aggrandizing comments. And I guarantee you, I wasn't making any cute quips either. I sure as h**l wasn't smiling.
I think one part of the problem comes from trying to frame things from the past in the context of today's world. The "Deck the Halls" example is perfect: Instead of using the opportunity to explain to kids that the word "gay" has changed in meaning, somehow it is preferable to let children misunderstand the word by using today's common definition. We sell our children short if we don't believe that they can comprehend that language can (and does) evolve.
We should use these cultural artifacts to understand the past. Once we understand how society has evolved, we can use that knowledge to make our future better.
I do find it funny how many people abhor politics and politicians... but those same people will jump right on to the "Political correctness" bandwagon. Apparently, no one thinks about where the term comes from... The idea being that politicians have to be able to speak in euphemisms and use vocabulary that will avoid possibly offending anyone at all. How's that for irony.
And one other point- - there no such thing as "a little rapey" ... it's like being a little bit of a virgin.... It either is rape or it's not. Period. Full stop.