There are a few different ways you can make your hair look greasy and unwashed. One way is to not wash your hair for a few days, and to not use any products in it. This will give your hair a greasy, stringy appearance. Another way is to use a little bit of oil or grease on your hair, which will make it look greasy and unwashed. Finally, you can try using some dry shampoo on your roots, which will Absorb excess oil and give your hair a dirty look.