All of these interpretations are my own opinion. These could be completely wrong.
I always thought this song was about Pete.
"Show me a starry-eyed kid. I will break his jaw."
I think this is funny because Pete himself at the time was a starry-eyed kid. This is evidenced by,
"I will save him from himself. Here's a picture with a note--'Don't turn out like me,' it's only for your own good."
I think this is referring to the starry-eyed comment, Pete is warning against becoming a "starry-eyed," like is.
"Haven't you heard? The word on the street is I lost it, called it quits."
This is an example of gossip Pete's heard, which leads into the next lyric.
"Get out into the sun, out from behind the gossip."
This is referring to people who hide behind the "shade" of gossip, he's basically saying, "show yourself, coward. Step into the light where I can see you.
"This story's getting old, the homewrecker with a heart of gold."
This could be in reference to a cliche from the music or film industry, or it could be a callout to someone Pete knows personally. Maybe the guy Jeanae White cheated on Pete with.
"Keep you locked up in the trunk of my mind."
This is just a lyric I really like. I like the negative image of cherishing someone, like you're keeping the thought of them hostage in your brain.
"Keep talking, keep this alive."
This could be interpreted in two ways: the press fueling Fall Out Boy's popularity by reporting on them (good or bad press doesn't matter), or the image of Pete begging a lover to keep in contact because it's the only thing keeping the relationship alive.
"Even when there's nothing worth living for, you're still worth lying for. No one has to know."
I also really love this lyric. In the first part of the first sentence, Pete could be talking about one of the dips in his mood swings. Pete has bipolar disorder, and this could be in reference to one of his bad moments where he feels hopeless. I think the second part of the first sentence and the second sentence could refer to a secret tryst with a lover.