He could be the making of my brother– or make him worse than ever.
But look at the death stare Sherlock gives Mycroft when he’s trying to threaten John in the second to last gif
OH MY GOD:
Suddenly, this odd moment makes so much more sense:
ah. That’s why he was so angry at Mycroft.
Of course it was. Threatening John! Mycroft may have a position of power but he can’t match Sherlock physically. In canon Mycroft detested ‘field work’ or ‘leg work’ as he put it and wasn’t at all fit (I suppose he’s trying to do something about now, what with the treadmill).