system
Given the following post, respond as if you're commenting on Reddit:
human
[Borderlands 2] What is up with the Goliaths?

Is there an explanation as to what/how they can pop out their whole skull and spine and why it causes them to go into a rage?  Is it from Eridium exposure?
gpt
You need to look at the history of Pandora.  Most humans on the planet were slave labor (mostly prisoners) to operate mining sites.

After the corporations pulled out (too costly to maintain) they left the workers to fend for themselves.

This harsh environment took a toll on their psyches.  This is why there are so many exceptionally insane individuals.  The goliaths are such individuals. 

Eridium exposure, strange mining chemicals, harsh environments and such are likely the cause of biological abnormalities.

The goliaths are unique in that they're "passable" except for their heads.  So they wear helmets to cover their deformation.   When they are exposed, the pain (physical and emotional) causes them to enter a mutating rage.