JIMothy is reserved for when Bones wants to be a special type of asshole. It's when he's in peak 'southern belle' form. It's usually followed by raised eyebrows, a hand flying to his heart, and a fake surprised "why I never!" Spock stands by and huffs quietly at the displayed--the Vulcan equivalent of the snort before adding "to coin on of the good doctor's many phrases, 'bless your precious little heart,' JIMothy." And Jim just. Implodes a bit both from irritation and from affection overload.
Well goodness I’ve got a case of the vapours *fans self very southernly*