Well, I think it was sexual - because Cas had made out with Meg in the hallway - though, RAPE is a strong word, because Meg had initiated that kiss in the hallway and certainly didn't seem to mind it at all. Plus, they didn't need any information from Meg at all, the ONLY thing they wanted was to kill her.

Of course, it's all the intent behind the joke, and Dean didn't really mean that he'd wait to kill Meg so that she and Castiel could possibly have sex first - that would be ridiculous. It was just a stupid joke as Dean is wont to make.

But you know, rape culture and all that stuff - I think claudiapriscus and I hammered it out when it aired and it basically comes down to whether you want your television shows to actively work to progress society or if you want them to simply reflect it.