LINE OF ACTION: Smirk is taking a normal smile and adding a little smugness to it with a cocked brow and the smile coming out of only one side of the face. As if the character is saying, "You gotta be kidding me..." Sometimes a smirk comes out of holding back a smile or laughter.
DEFINITION: A smirk refers to a smile evoking insolence, scorn, or offensive smugness. An affected, often offensively self-satisfied smile. To smile in a self-satisfied or foolish manner