Seeing as he didn't mumble his way out of this video, he's probably fielded odder questions.
To be up and front about it: Newton's Second Law isn't your friend when you're doing the horizontal, or rather, free-floating tango. The Second Law, which involves accelerating masses, isn't much of a problem on Earth because there's always an equal force—gravity and your bed—keeping you from moving anywhere you don't want to.
But in space, where everyone and everything is free-floating, pushing into your partner would cause them to accelerate in that direction until they hit a wall. Obviously, this isn't conducive to sex in any way.
Tyson's solution for this? Belts. Lots of belts. Kinky connotations aside, while belts wouldn't make zero-g sex any less complicated, they would at least keep your partner, and you, from crashing into walls whenever either of you smacks into the other.