I'm gonna shrink my friend's sweater because I'm jealous of it.
Oh dear. What makes you think it's okay to damage your friend's sweater?
It's a sick sweater, and I wish I could wear it. They won't let me though.
If you like your friend's sweater so much, you should find out where they got it and buy one for yourself. Damaging it ruins your friendship and causes you to not be trusted anymore.
They deserve it for not letting me wear it.
If your friend doesn't feel comfortable with letting you wear their sweater, they don't have to. I know that can be frustrating, but I'm sure you can find that sweater in stores to buy one for yourself. Shrinking their sweater will just make them upset and guarantee they won't ever let you borrow their clothes in the future.