Lyric discussion by TdyYrLove 

On the surface, this song appears to be about teenage angst and sexual frustration. But what exactly is being added up?

This is a song about purchasing service from a prostitute. The boy is frustrated and wanting (why can't I get....). The purchase of the gun was necessary for him to go to the bad part of town (presumably where the prostitutes are).

Broken-down kitchen at the top of the stairs, Can I mix in with your affairs? Share a smoke, make a joke, Grasp and reach for a leg of hope -- Is describing the brothel.

Toward the end of the song, right before the act takes place, the prostitute says "wait a minute honey, I'm gonna add it up". She wants to count the money before performing service.

Mate, who's mum goes into town to buy them a gun so they can go to a rough bit of town to go and sh@g a prostitute in a brothel?

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