They're also seriously easy to make. If you have any knee-high socks (new or old), you can just cut them and cut a hole for your thumb (sewing that area is best so it doesn't wear out as fast), and BAM! armwarmers.
Some kid: "Why do you wear those all the time?"
Me: "To hide the scars, retard."
Some kid: "Wow. Freak. You're a cutter?"
Me: "Fuck off."