Hey Ashley, good to read that you are auditioning for your dream role. How about taking a really happy song and sing it completely negative? It is easy to do ...and everyone else will be singing negative things. They'll think you are the greatest thing since toast.
I Want To Be Happy comes to mind, so does Singin' In The Rain. Easy for the pianist, easy to sing, easy to make them double over with laughter.
Of course, I always say sing from the show since you already know the song, but this is such an easy and effective concept, and actually funnier than the song in the show, that I would change my usual recommendation this time.