Sharpies are tough.
Maybe Goof-off or whatever that stuff is called. I used it on my husband's jeans after we used oil based stain on the fence. Took about 3 days of soaking, rinsing with a hose and repeating until I finally washed the jeans about 3 times in the washer. They came out looking almost new.
Can you put a small patch over it? Or wear the shirt with Overalls. :)