So he didn't know. Well, that was probably a good thing.
"Okay look, we only ever properly do it in the backseat if we end up too drunk to get outta the car." Well. As 'properly' as you can while you're in a car. Sometimes you had to improvise with the space you're given.
"And I do clean up afterwards. I don't hose the entire thing with disinfectant and do swab tests but it's clean, okay?"
Maybe it would be better if Jamie didn't know how many times Ares was too drunk to get out of the car.