I am nasty
This is our fitted bed sheet after it was washed:

Yes, the same sheet. The top part is the normal color. The bottom part is where I lay. Yes, that’s after washing.
I ran the sheets through again, this time using hot water, the fiercest mode available, real bleach, and detergent with color-safe bleach. Not much better:

Yuck. This is a 100% cotton sheet set. My wife’s side is pristine.
Yes, I bathe daily.
Pre-soak in soapy water. Thats what laundry tubs are for.
Billy Mays would suggest Oxiclean… http://en.wikipedia.org/wiki/OxiClean
Or quit hanging out with all of those Republicans. They can make you feel awfully dirty pretty quickly, and maybe they are… :-P