The Johns say:

Performed at the breakneck tempo of "classic new wave," this song is the harangue of an embattled old-timer who refuses to yield the floor. Chorus: "I'm not done, and I won't be till my head falls off." Check out the rock power of bassist Graham Maby in the breakdown section.

Quoth Josh Ward <ward@umr.edu>:

There were 87 Advil in the bottle now there's 30 left
I ate 47 so what happened to the other 10?

47?? That's a lot of Advil! I would guess that the narrator is trying to overdose. The fact that he remembers how many he took exhibits a great memory.

Why do you suspiciously change the subject and break my concentration
As I dump the bottle out and I count the Advil up again?

Perhaps the other person is trying to get him to think about life, and staying alive.

Don't interrupt me as I struggle to complete this thought
Have some respect for someone more forgetful than yourself

And I'm not done
And I won't be till my head falls off

He's not going to give up until he's passed on

Hitting every pocket on my shirt, pants and overcoat
And I'm hitting them again but I don't know where I put my notes

Looking for a suicide note, as the effects of the overdose take him?

Clearing my throat, and gripping the lectern I smile and face my audience
Clearing his throat and smiling with his hands on the bathroom sink

He's looking into the bathroom mirror, and struggling to look strong in his last moments...

And when I lean my head against the frosted shower stall
I see stuff through the glass that I don't recognize at all

He's getting close to the end now. Are hallucinations seen after taking 47 advil?

And I'm not done
And I won't be till my head falls off
Though it may not be a long way off

Closer than he thinks, probably

And when I lean my head against the frosted shower stall
I see a broken figure silhouetted on the wall

Perhaps the figure that he sees silhouetted is missing it's head, showing that his head has fallen off.