Brain Age (DS)
Of course, you're only cheating yourself if you cheat at Brain Age, but there's still a lot of fun to be had too...
When the speed ranking screen comes up, tap the picture of the man walking or the rocket taking off and you'll hear a noise - including some music from Mario!
On the title screen, say "glasses, glasses" into the microphone and Dr. Kawashima will flap his glasses at you.
If there is a question that may take you a few seconds to answer, close the DS, think it over, open the DS and write the answer - game time freezes when the DS is closed.
Select a save game slot and hold Select while choosing the Brain Age option to have the option of selecting the order of the Brain Age Check tests.
Finally, the game can't see what you're doing, so you could just write down all the words in the memory game and then write them back in... but we'll leave that up to your conscience to decide whether you should try that or not!
For even sadder ways to cheat at improving your brain power, head here.