This is sooo easy. And it can be such a problem if you live in a house with shedding cats or dogs, especially if they have white fur.
Use a one-sided razor blade. These are used by painters to scrape paint off windows. If you don’t have one, look for them in a hardware store or paint store. Then just lay your garment out on a flat surface and gently scrape. Use a piece of scotch tape to hold the gathered fluff.