The problem with Strange being a gloaty egomaniac with a stick up his butt is that he assumes that everybody else will retaliate in the same way that he does: being an asshole, sniping back and forth at each other, and passive aggression. He doesn't expect actual aggression.

Rita's fist connects and it connects hard. There's a satisfying thud as her fist connects, followed by Strange stumbling backwards slightly. Needless to say, he was not expecting that in the slightest. Gingerly, Strange prods at his jaw, opening and closing it experimentally. Nothing seems to be broken, but it hurts like a bitch.

"What the fuck was that for?!" It's a stupid question because really Strange, what the fuck do you think it was for, but he's still a bit taken aback by the fact that he actually got punched. Noticeably, he's not making any attempt to swing a punch at Rita himself because he is a gentleman and gentlemen don't get into fist fights and really, it's not like he'd be able to hit her in the first place. Strange knows his limitations and one of them is punching.