This is an undated photo of Ethan Couch published by the U.S. Marshal Service.
When Couch was 16 he killed four pedestrians and seriously injured two others while drunk driving. Although he was convicted for this, he avoided prison time and was sentenced to ten years probation. As a defense tactic, his attorney successfully argued that Couch suffered from "Affluenza" (e.g., The inability to link bad behavior with consequences because of his parents teaching Couch that wealth buys privilege).
Ethan Couch is currently 18 years old and is the subject of a manhunt since 11 December 2015 when his probation officer was unable to contact him.
Context is paramount when determining the meaning of any nonverbal behavior - and this fundamental cannot be overemphasized. Yet in addition to the image above, there are a good number of images of Ethan Couch with similar facial expressions in the context of various legal settings (court, pre or post-court contexts, etc).
Displaying this expression during legal proceedings when four people have been killed is certainly an example of smiling out-out-of-context - which is a form of "Duping Delight" (Ekman). This pattern suggests that Ethan Couch either believed he was fooling others into believing a false narrative (and he takes sincere joy in doing so - which he cannot hide - and his joy "leaks" out in the form of a suppressed smile) - and/or he has a clandestine plan (which of course now he has implemented).
For some, it may be difficult to believe, yet this is a common facial expression displayed by a fair percentage of criminal perpetrators.
Nonverbal Communication Analysis No. 3411: Donald Trump's Vulgarity, "Schlonged" and Body Language Tells
Nonverbal Communication Analysis No. 3403: "Johnnie Walker - Dear Brother" Commercial
Nonverbal Communication Analysis No. 3398: Orangutan Sees a Magic Trick - Bonding, Rapport and Laughter - Body Language
Nonverbal Communication Analysis No. 3385: Adele, "Hello" and SNL
Nonverbal Communication Analysis No. 2932: Fred Couch ("Affluenza" Father) Arrested and a Body Language Signal of ....