I always get excited ( steady on ) when someone chews their nails, or puts their hand over their mouth, or leans on their hand. Anything that puts the fingers near the face, then you get double the pleasure of sketching.
Hands are brilliant to draw, get them right ( not often ) and they look great - get them wrong ( here ? ) and they haunt you forever. I try to use the knuckles to describe them, but always get the heel of the hand, and how it connects to the wrist, way off.
And ears as well. I usually just let a quick squiggle tell the story, but you could really get into the folds and shading of peoples ears.
This was also drawn on a train ride home. It was in the summer, and there was a very argumental couple dominating the carriage, and this bloke was doing his level best to ignore them, staring fixedly out the window.