If someone is smirkier, they are showing a smug or self-satisfied smile.
Being smirkier is usually not a very nice thing. It can make people feel annoyed or think the person is being mean.
Examples:
She looked at me with a smirkier face.
He gets even smirkier when he knows he's right.
The cat looked even smirkier after catching the mouse.
The dog looked even smirkier after stealing the treat.
The villain became even smirkier after capturing the hero.
The boy became even smirkier after winning the game.