It could be an NPC that speaks l33t, he could be off in a corner by himself, the other NPCs could speak of him with pity, and you could have to use l33t to finish a simple, extra-credit quest with him. He would have to use some iteration of the "all your xxx belong to us". Best way to teach is by example, what not to be. It might be fun enough that people would remember it. Short and sweet, though.