In the Crucible Why is Rev. Passis walking around with a "mad" look on his face?

If you mean Rev. PARRIS, I think it is because he realizes that he holds these fate of the accused in his hands. Not just with regard to their earthly life, but in the more important hereafter. What many students may have trouble imagining in modern times is how seriously these matters were taken back then. These people moved across a great ocean to unknown lands just to be able to worship their God in their way. Nothing was taken more seriously in that time than the ultimate fate of one's soul.

Couple this with the fact that the Rev. really believed that there were demons/witches afoot who sought to undermine all Godly works, and you can see why he was a man who felt himself to be the only thing between the Devil and his parishioners, between eternity in Heaven or in Hell. No wonder he was crabby!