My friend said that kriss blades were designed to break off inside the "bad guy" after he has been stabbed by it.
No.
Many people ask if the wavy shape of a Kris blade is just for decoration. The answer is certainly no. The Kris is of Indonesian origin. These people don't have money for wall-hangers.
The Kris shape allows a blade to have more cutting edge in the same overall length.
Furthermore, if a conventional knife hits something hard when stabbing, say -- just for example -- a bone, it will probably stop. But, thanks to its curved shape, a Kris tends to slide off the bone and continue in deeper.
Finally, the Kris shape makes the blade wider without making it heavier. A wider blade makes a wider wound, but a wider blade is usually heavier and, therefore, harder to handle and move quickly. A Kris is the best of both worlds, light and wide.
So, while not practical for many every-day cutting chores, the shape of a Kris is hardly for decoration.