Recurring theme:

Excessive use of the word "insouciant"

Joyland

Spoiler alert, but a certain someone's trademark insouciant tip of his hat is how you figure out he's the bad guy.

Mr Mercedes

Duma Key

Jack shrugs his shoulders in an attempt at insouciance after a particularly harrowing interaction.

The Dark Tower IV: Wizard and Glass

The Talisman

"Richard shrugged, and despite the insouciance of the gesture, his face was miserable"; "Her insouciant go-to-hell grin was, however, all her own"