He might not be psychotic, but he has anger management issues and an inferiority complex. The best you can say is that he's unstable. Everyone else is dealing with Phillip's ranting and raving and "leadership." If he wants to author his own exit, then break something, douse the fire, yell and scream at everybody but don't sabotage everyone else's chance at the game. By dumping the food, he put their strength and health in jeopardy. And based on his teammates demeanor, especially the women, you can tell that they were traumatized. I felt uncomfortable watching the episode. I'm sure the show will provide some way for them to gain back the food supplies, but there will probably be a cost.
And of course I do think he sealed his fate, which may have been the idea -- he certainly was toying with quitting anyway. But I saw both Brandon and Phillip getting mad -- neither one controlling it very well, though Phillip undoubtedly allowed self-preservation to play a greater role in whatever control he did exhibit.
I will agree that overall Brandon could be characterized as "unstable" -- meaning highly mercurial, unpredictable, and with wider mood swings than are generally normative, though not to "fatal" degree -- meaning that his temperment was manageable, by himself and the tribe. That said, I found him remarkably, and somewhat unexpectedly, restrained throughout most of the last installment -- even approaching preposterously arrogant Phillip and playing the diplomat at one point.
What I react to though, is people leaping up to affirm that yes, Brandon certainly is a complete psycho, blah blah blah. That assertion itself is off the deep end for me...