Meaning
Half-lidded eyes glancing to one side and a lopsided smile pulled up at one corner. The smirk carries smug confidence, sly knowledge or a flirtatious hint, the look of someone who knows more than they are saying.
Among friends it marks innuendo, bragging or “told you so” moments: “Guess who finally beat you at chess 😏” In flirting it adds a suggestive edge, which is exactly why it can backfire with coworkers or family. It may also come across as condescending in a disagreement, where it seems to say you feel superior.