the smile that won't turn off
A permanent smile that always seemed like he was trying not to but just couldn't help it. His Da always formerly saying to Wipe it off.
Context
Matty's face broadcasts a grin he can neither summon nor stop, a mask fused to the face so early it reads as insolence rather than damage — the father's standing order to "Wipe it off" a lifelong losing battle against an expression that means nothing Matty intends. Like Hal's grimace-smile in the opening interview, the face has become a sign that transmits the wrong thing on its own, independent of the person behind it.