As useless as it may be, I trash talk the AI (CPU, whatever). I don't trash talk human players, but when the game itself pisses me off, I'll call it cheap and throw a fit.
I've also been known to plead with God that I beat such and such opponent/level/challenge/etc. Again, this is something I do when I'm alone, not when someone's there watching or playing.
Finally, when I'm feeling cocky, I often quote movies, wrestlers, videogame characters from other games and others with awesome catchphrases. This I tend to do whether someone's there or not. In fact, it's more fun to do when others are around to catch the references.