I recognise that Leonard may not exactly be the Prom Queen around these parts, owing to his rather Dickensian Arctic activities, and general moral dubiousness, but he occasionally redeems himself (once in a Blue Baboon), and almost exclusively with regards his relationship with Sheldon. As a couple, moreover, they’re so believable it's damn near cliché. I sometimes suspect Sheldon actually thinks he IS in a relationship with Leonard…or at least in some species of S/P/L threesome. The mind, boggle it does. (Mildly pleasantly in my case...)
Anyroad, as I sense that the recent episode had a screed of Shelnard decency about it, let’s begin with;

Her withering glance has been known to freeze a genius or two. Or three. Or four. (Look at Leonard doing the Sarcasm Dance. Hee!)

Alright humans, we hereby encourage you to post your favourite Sheldonic expressions and mannerisms, from demented to charming, with a pit-stop at wholly unsettling. With your help, we shall build a scroll of terrifying mirth, to titillate the ancient, and chasten the young.
Start.