I can think of a fair few thixotropic things, but none that are actually solid before agitation. Ketchup is famously thixotropic - won't flow out of the bottle until you bash it, then it gushes out all over your chips.
Quick search suggests that some yoghurts can be nearly solid thixotropes and go liquid with stirring (need more stirring than just a quick stir though) and will revert back to solids slowly at rest.