The thing about Mycroft is that he's not Greg's type, not even remotely. Greg's never gone for posh blokes, never gone for a man he couldn't imagine having a beer with before they fuck. When he'd first met Mycroft he'd pegged the man as yet another stuffed-shirt administrative type, contributing nothing much to society except a mile-high stack of paperwork and a smug smile, and it was only finding out that he was Sherlock's brother that made Greg look at him any more closely than that.
And now... now when he sees Mycroft, all he can think about is the fierce gleam in Mycroft's eyes as they tussle for dominance before tumbling onto the sheets, the way their tongues and teeth clash together when they kiss. He thinks about Mycroft's hands, slim-fingered and smooth but no less strong for that, clenched in Greg's hair and drawing his head back as Mycroft slides into him, slick and hard and demanding.
Mycroft without his impeccably-tailored suits is a different person entirely, a man instead of a sexless civil servant. Greg loves the dark trail of hair down the center of his belly to his cock, loves the flush that spreads over his face and neck and chest when Greg is sucking him off, loves the way Mycroft is happy to rim him for ages, fucking Greg's arse with his tongue and biting the edges of his hole until Greg is sweat-drenched and moaning and fucking desperate to come.
And yeah, he still can't imagine having a beer with Mycroft – can't really imagine socializing with him at all, really – but given that the sight of the man, even all buttoned up, is enough to make him instantly hard? Greg's beginning to think that there's something to be said for skipping the pleasantries.