It seems to me the irony in the last stanza of the poem stems from this line: "to look into your soul." The English teacher is finally allowing students the freedom to explore and examine and reflect (much to the nerdy student's dismay, as he's the one who only loves true and false, right and wrong). The second stanza sets the reader up for great things. It's a sunny day, students are gleefully cheering, they get to have class outside--and the studies will revolve around poetry. Everything sounds like it will be a glorious time of reading and writing poetry, of introspection and discovery. Only the nerdy student shudders at the thought, perhaps understanding that what he will soon discover is not going to be pleasant. That's why the last stanza is ironic--the much hoped for break from facts and data and the opportunity for introspection (self-examination) has led to self-discovery, and what they find isn't pretty. In fact,
the cheers subside
quicker than you can say
please shoot me
just shoot me now and put me out of my misery.
The joy is gone in the face of discovering what lives inside our hearts and souls. This is, of course, a one-sided view of the power of poetry, for it also has the power to inspire and create passion where there was none. In this poem, though, poetry is used as a mirror into what we'd prefer not to see in our own souls.