Btw, if you actually want to play this prank on someone, here are the Windows EXEs:
It will say 1 of 12 random confirmations if you type any sentence into the command prompt starting with the word Should, Can, or Is. Of course for this to work anywhere, you'd have to place these files in a folder that can be accessed from anywhere (e.g. c:\Windows or any folder set in your environment PATH).
The source code is yes.c
if you want to compile yourself.