Imagine being an acquaintance of Tweek's family, and you are staying with them for a couple of week's because your house is under renovation or some shit. Imagine accidentally walking in Tweek when he's changing clothes in his room, making him nervous around you in his own house. He starts changing in bathroom behind a locked door so you can no longer see his ripe body, but that won't stop you.
Imagine going through Tweek's underwear when he's not in his room, stealing them and rubbing them against your face. Imagine smelling the heavenly scent of him. Maybe you can't resist the urge of pleasuring yourself with them? He notices his underwear are missing again, but the thinks it's because of the gnomes.
One day when you're pleasuring yourself with his underwear again, you don't notice him coming in his room. When he notices what you are doing, he starts crying and panicking and begs you to leave. That's when it's your time to pounce on him and take his beautiful body.