Martin Schenk sweating a perp without even raising his voice.
Luther, his hand nailed to a table, pulls the nail out with his other hand.
Cameron Pell's downfall. When he kidnaps a school bus of kids, intending to suffocate them with engine smoke, one boy slips away. He tussles with him and loses his mask. Luther and Justin arrive in time, the boy being held at knifepoint. Luther forces a Villainous Breakdown on Cameron by completely ignoring him and throwing away his mask, talking to the boy and walking without a care in the world to the kidnapped children. Then, to finish it up, the hostage escapes with ease and Ripley clocks him in the face.
John using Jenny's accidental murder of Toby to his advantage - he no longer has anyone blackmailing him and after he frames Frank for the killing, Toby's grandma has no leverage against him. Also, he makes her back off by invoking Alice Morgan. We don't know if they actually spoke about it, but one could be pretty sure it would barely took one phone call for her to make good on that promise.
Idris Elba winning a Golden Globe for "Best Actor In A Miniseries". YMMV, but his acting was pretty damn awesome.
Benny showing serial-killer Carney a picture of Luther and the three women he had sent Paul to kill giving him the finger is this and a Moment of Funny aswell.