I guess Kirk was not that smooth-talking by that point in his life (well, he certainly was not 3 years before in the bar)... I took it as something that he said because he didn't know what else to say.
But it was obviously also a setup for the beautiful girl to turn the lights on, so the audience gets to see that she's a green alien.. punchline "Did you just say, "this is so weird"?"
It didn't...Kirk didn't have sex with an Orion in TOS ...as a matter of fact his playboy reputation is perhaps unwarranted. Recently saw a website (courtesy of Indranee) where someone broke down Kirk's sex action episode by episode.....more often than not he used his charm with the ladies to get the Enterprise out of a jam...not to satisfy his own desires and wants.
He came close to being seduced by one in Whom Gods Destroy... but then she ruined it by trying to kill him!
It's true that he did not have that much sex... in some cases he flirted with some alien/android/crazy women for other purposes... and in a couple others, he actually fell in love but didn't get to do anything before the woman (or female android) tragically (and so conviently for the show) dies... The curse of disposable love interests!