a person who is embarrassed to shit in public restrooms, or one who is embarrassed to shit when other people are close by.
He would never go to the bathroom when other people were around, he'd hold it all day long till he got home from work and would let it go. That man is a shy shitter.
This is when someone says they'll shit on your chest, but they just squat over you and fart for ten minutes.
This chick I met was a shy shitter so I was sucking gas all night!