I promise, its GOD, not GUN, no matter what you hear.
I'm NOT changing it.

Proof :

on Fall Out Boy's MySpace, which is maintained by Adam (from Fueled by Ramen)

Is it "loaded gun complex" or "loaded god complex"?

Despite what you read on livejournal, a messageboard
or myspace, it's "loaded god complex."

And he told me in person. Don't call me stupid...its loaded GOD.
If you have no idea what that is, go listen to Gym Class Heroes.

**added note**

A God complex is a colloquial term used to portray
a perceived character flaw as if it was a 'psychological complex'.
The person who is said to have a 'God complex'
does not believe he is God, but is said to act
so arrogantly that he might as well believe he is God
or appointed to act by God. **from wikipedia.com**

if you look at the other lyrics on the cd such as "i've got arrogance down to a science"
it makes perfect sense