"The Kubrick Stare"

This analysis from Far Out:

However, the most notable trademark used by the director is the iconic Kubrick stare. The technique can be traced in almost all of his films, although it finds its ‘official’ origins in A Clockwork Orange. Throughout the movie, Malcolm McDowell’s menacing protagonist, Alex DeLarge, glances at the camera with a terrifying stare as if acknowledging the audience’s presence...

However, the iconic look, soon dubbed the ‘Kubrick stare’, shortly became its own form of cinematic shorthand. Other directors began incorporating the stare into their work, and movie buffs quickly recognised examples of the Kubrick stare in films that predated the director’s establishment of the specific gaze. For example, Anthony Perkins’ Norman Bates gives a particularly chilling look in Psycho that many have classed as a Kubrick stare. 

Notable modern uses of the Kubrick stare can be found in David Fincher’s Gone Girl, Christopher Nolan’s The Dark Knight courtesy of Heath Ledger’s Joker, and Jonathan Demme’s The Silence of the Lambs. So, why is there so much significance placed on this iconic stare? It’s a simple look, yet the meaning it conveys is vital. It typically signifies that the character is unstable and deranged. When an actor performs the Kubrick stare, something intense will likely take place. Due to the technique’s recognisable status, when it is used in non-Kubrick-directed films, audiences can still interpret its meaning the same.

And this from TV Tropes:

The Kubrick Stare is really quite simple to pull off. You simply do the following:

1. Tilt head down

2. Look up beneath eyebrows

...and voila! Instant super-creepy look!

It generally signifies that the character in question is either really, really pissed or really, really deranged, and the person they're looking at is really, really screwed. Other times — usually when combined with a smile — it means they're feeling really, really clever (regardless of whether or not they actually are).

A compilation: