How does kyon post a threat to lucion or whatever his name is

Because Lucaon lowers his guard when he's with Kyon, which is something someone could take advantage of in order to hurt him. And that's exactly what happened: Kyon convinced Lucaon, who never eats actual food but energetic pills only, to eat food with him, and someone saw it and took the chance to slip a poison in Lucaon's meal.