When someone smerks, they smile in a smug or self-satisfied way.
Smerking can be seen as a little bit rude or annoying because it shows someone is feeling a little too proud of themselves.
Examples:
She smerks when she wins the game.
He always smerks when he gets his way.
The cat smerks after catching the mouse.
The little boy smerks when he gets a cookie.
The villain smerks after capturing the hero.
The fox smerks as he outsmarts the farmer.