The fact that Darius didn't acquiesce on the first 'let me out' is a large part of what has me concerned. I can think of three possible reasons in that context as to why Darius would be grinning alongside his boyfriend's quite obvious anger, and if I know Darius as well as I think I do, what I would consider least forgivable of the three... that Darius was deliberately provoking MC's anger for his own amusement... is also probably the most likely.
I agree with you on one point, there's no indication that Darius was planning on leaving MC there... and it could be you're right about me, too, now that I think on it; maybe I am being over-critical... but there's also no indication of how far Darius was planning to go with this before releasing MC, and even if the scene hadn't ended on that note, I ain't the sort as can trust someone who's willing to piss off their SO for a laugh; there's always part of me that wonders how much worse they might get in the future.