He's straight up talking about sex. And Strange is a jerk, he badly repressed a laugh as 9S starts blushing. Is this the wrong time to be teasing the android about sex? Probably! Is he going to do it anyway? Definitely.

At least he's going to explain things before 9S throws something at his head.

"It's a euphemism," Strange explains, with a grin. "Not as fun as other euphemisms, but basically, to ride someone is another way of saying to have sex."