What is the meaning of "A.C. or D.C.?"

In Heinlein's A stranger in a strange land, there is a moment when nurse Jill kisses Martian man named Mike and another man, Jubal, puts a comment on it. It comes as follows:

“Son,” he said, “you amaze me. I would have expected you to curl up in one of your faints.”

“I so did,” Mike answered seriously, without letting go, “on first kissing time.”

“Well! Congratulations, Jill. A.C., or D.C.?”

“Jubal, you’re a tease but I love you anyhow and refuse to let you get my goat. Mike got a little upset once—but no longer, as you can see.”

The only meaning of AC and DC I found was alternating current and direct current, but it is about electric power distribution and is definitely not my case. I have no idea about meaning and genesis of Jubal's mockery. Can anyone, please, explain it to me?

Don't pay attention to Mike's strange language - he is the Man from Mars and has a different native language and way of thinking.

Solution 1:

In my youth (the 1960s and 1970s) AC/DC was a euphemism for bisexual. As far as I recall AC meant heterosexual and DC meant homosexual (derived from Alternating current and Direct current) and I suspect that Heinlein is using it in this way as the book dates from that period.

Solution 2:

AC/DC refers to the two main types of electric power.

However, it's used humorously to mean "straight" versus "homosexual" sexual orientation.

It's that simple.

(Note that one of the world's most famous rock bands, is called "AC/DC" ... as well as referring to "electricity," as in electric instruments, it's a sexually-charged term.)