Lyrics:

I think this is the song you're talking about, it was played during the prom scene but it's called 'Flightless Bird, American Mouth' by Iron Wine.
The lyrics are:

I was a quick wet boy, diving too deep for coins
All of your street light eyes wide on my plastic toys
Then when the cops closed the fair, I cut my long baby hair
Stole me a dog-eared map and called for you everywhere

Have I found you
Flightless bird, jealous, weeping or lost you, american mouth
Big pill looming

Now I'm a fat house cat
Nursing my sore blunt tongue
Watching the warm poison rats curl through the wide fence cracks
Pissing on magazine photos
Those fishing lures thrown in the cold
And clean blood of Christ mountain stream

Have I found you
Flightless bird, grounded, bleeding or lost you, american mouth
Big pill stuck going down