Deliberately Forcing the Game to Crash

I don't think that's possible in a "safe" way - however, a "crash" is, by definition, an unwanted behaviour of an application: this implies that's impossible to "planning" it. Even if you hack the memory consuming (that's very not reccomended!), you can 't be sure to obtain the same behaviour on different machines, or if your game will be played 5-6 years after its creation, on more powerful machines.

For your purpose, I will acting in a different way (maybe less "stunning" for the final user): save the game, pop up a text like "This character is too awesome! Your game will be closed in a moment, 'cause it cannot handle that...) - or something similar -, wait for some seconds with a "yield WaitForSeconds()", to allow the player to read that, and then close the application with "Application.Quit()".

EDIT (another idea): Sorry for re-open that, already closed, question. But I've just had another idea, and maybe you could be interested. Take a snapshot of a Windows error popup, and make it as a texture. "Paste" it onto a plane, and make a new scene in which you visualize that plane. You have just made a fake error popup. When you encounter that character, save the game, unload the actual scene, and load the scene that I've just explained! Then, if the player click in proximity of the "OK" button, you will close the application with Application.Quit(). Pay attention, you also have to adapt the resolution of the application at run time (look here), to make a credible popup. It's just a Photoshop trick and, obviously, a Mac standalone would be a little out of place in the end, with a Windows error! ;)