Mine depends on my mood and whats going on in my life at the moment....I don't know I say "thats my song," to a lot of songs but they all have different themes to them...Good question I agree but I will have to get back to ya on that one.
Ohh maybe today my theme song could be "Bang on the Drum," or as my group Vocal Trash (awsome group btw) sings "Bang on the Can."