There is no single documented source for this mashup, so it is best understood as online meme slang rather than a line from one show or film. It joins sussy, a playful shortening of suspicious popularised in gaming and social video culture, with sigma boy, a label for exaggerated, self-assured confidence. Together the words work as a shorthand joke: one glance tells viewers the person is both dodgy and oddly proud of it. That simple, repeatable contrast is why editors keep reusing it across short-form clips, reactions and gaming edits.