Who doesn't have a T-shirt, sweatshirt or pair of jeans and/or shorts that has a stain you can't remove. Instead of throwing it out paint something over it. Make it look intentional by adding more designs to match on other areas. Or paint the same design on a pair of jeans to match the T-shirt design you just painted so it looks like a set. Add the design to the sleeves, around the hem on a pocket, etc. so it looks like it was intentional & evens out the pattern.
Wash the garment but do not use any fabric softner on it. You can use regular acrylic paint that you buy at a craft store and adding a "fabric medium" to it. Just add a few drops of the medium to your acrylic paint as you paint your design. You can also buy fabric paint that is just for use on fabric. It makes the paint soft & spread more easily. After paint is good and dry set the paint with a hot iron. Place a cloth over the painting area & hold the iron over the paint for a few seconds & move to cover the entire area that you painted. Do not slide the iron back & forth, just hold it for a few seconds before moving to the next area. Garment is machine washable & dryable.
If you are not artistic you can simple make simple things like stars, dots, stripes, flags or other easy designs. A child's simple "flower" coloring design is so simple anyone can do it. If you make a mistake quickly use water & a little soap to remove it by patting it off. Do not spread the paint by using a back & forth motion.