This brand name, "Sharpie" is used to talk about any type of permanent marker, like how we call all band-aids "Band-Aids", by the brand name, regardless of the actual name of the product.
Torch: What is it?
Slash: I think...you're addicted to sharpies.
Torch: What? No I aint.
Slash: Uh, you're sniffing it right now.
4. permently screwing up ppls home work
Reid: Relax, it was just a prank.
Chris: WTF THIS IS PERMANENT!!!!
Reid: Hehe Woops.