This clip is making the rounds and confusing viewers all over the internet. However, the simple explanation is what's known in physics as the Rehbinder Effect.
The Rehbinder Effect is the reduction in the hardness and ductility of a material. Therefore reducing the surface energy. In the video we see a demonstration of the effect.
Obviously if you just go wild and start hammering at a ceramic mug, you're probably going to hurt yourself and without a doubt the mug is going to crack.
is cool AF. By submerging the mug under water, you're reducing the ductility and the hardness of the ceramic. As the video shows, it is fairly simple to hammer a nail through and create a hole in the mug.
So if you're looking to get rid of some old coffee mugs, or just want to mess with your friends this is a great way to do it.