What would cause a drinking gl to explode with juice in it?

Tempered gl can explode spontaneously, or at least in a way that appears spontaneous. It happens to sliding door gl and to car windows. What happens is that the surface tension of the gl is stressed in some way(temperature change, scratches, chips or dings) and the gl becomes unstable. There isn't as much tension holding it together any more. Not all that common in drinking gles but not unknown. If you drop a tempered glass on a hard floor and it breaks, it will probably explode and pieces fly all over. Regular glass will break in the same situation but not with as much force.