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