Dots and Boxes
I once got paid real money to write a Dots and Boxes program (see http://en.wikipedia.org/wiki/Dots_and_Boxes). This game is NP-hard, according to Berlekemp et al's Winning Ways (p.534). But I didn't use any of the sophisticated approximate solutions that have been developed for such problems, I just tried to steer the game to one of the positions that the program could analyse in polynomial time.
The result was that I was the only human who could beat it on a large board, because I knew how to frustrate its goals.
Biting the hand that feeds IT
