For anyone who doesn't want to watch the video (but do watch it, because I'm a big proponent of context being crucial when it comes to jokes, so there's really no wiggle room here — it starts at about 2:29), here's the back-and-forth:
Interviewer: "Would you rather go on a date with a dwarf, a hobbit or an elf?"
Martin Freeman: Elf. Definitely!
MF: Because look at them! They're beautiful. Yeah, men or women!
I: And the height difference doesn't matter?
MF: Not at all. I got a ladder. And I've got drugs. I can just make them. Slip them something in their goblet. Some will get offended by that now, because they'll call it "rape" or whatever. But, you know, for me it's a helping hand. Maybe I should stop talking. [laughs]
Martin, I'm going to let you respond to this one:
Update: I know Tumblr loves Sherlock, but here are some comments from people who really, really don't get it: