Have you ever discovered a mysterious grease stain on your clothing, in a spot where you're sure you never spilled any food? It happens a lot to dress shirts. Something like this:
It's from your dryer sheets. When you dry your laundry, be sure to throw the sheet in just before you turn the dryer on, and never on top of something you don't want stained. Think socks, underwear or towels.
And if you ever do get a real grease stain from food, try Dawn dishwashing liquid.